Great. Thanks very much and and welcome everybody. It's always really fun to do these webinars and, although I've done quite a few, over the years, this is the first one I've done that's actually been about feline oncology.

So, here at Colorado State, actually, cats kind of get short shrift. They only account for about 15% of our case load. So it's actually really fun to, get a chance to talk more specifically about cats and sort of remind myself of some of the things that I may have forgotten over the years since we end up seeing so few cats here.

So, yeah, we're, we're gonna do 3 hours, right in a row about feline oncology this afternoon, it's actually this morning for me, but, so we're really looking forward to that and I'm actually hoping to, to learn quite a bit from Sue's lecture as well. So, so on we go. Conflict of interest statement.

So I will mention, very, very briefly, a new lymphoma drug that's, that's approved for the use of, for the treatment of lymphoma in dogs called Tinovia. And Tanovia is, is, made or, or sold by a company called VETDC here in the United States. And I am involved withEDC so that's really the only conflict that's relevant for this hour.

So one of the questions that we often get from owners, when we have an animal that's been diagnosed with lymphoma is, is right off the bat, why did my cat get lymphoma? Was I feeding the wrong food? Should I have my house checked for radon?

Or is it the lawn chemicals that I use, those kinds of things? And, you know, I think the one that we all are very, very familiar with, especially those of us who've been around for a bit, is the association with the feline retroviruses, feline leukaemia and, and feline AIDS and the development of lymphoma. And we'll talk more about that in just a second.

One of the more interesting ones actually comes from, from Tufts University here in the United States that's now almost 15 years old, that actually looks at it at an association between gastrointestinal lymphoma and environmental tobacco smoke. So if cats come from, from smoking households, Their risk of lymphoma is actually higher. And, and right off the bat, that doesn't quite seem to make a lot of intuitive sense.

Until you look at the little picture down on the right-hand corner there, and we remember that, you know, the majority of cats that we see are actually compulsive groomers. And the particulates that, that are floating around in the air from, from cigarette smoke actually land on the cat's fur and are then ingested as part of the grooming process, and it's actually thought. That it's that process that contributes to the increased risk of lymphoma in cats that come from smoking households.

So just a few words about feline leukaemia, feline AIDS. So, in the, in the sort of the pre, feline leukaemia test and vaccine era, about 70% of the cats that we saw with lymphoma actually had feline leukaemia. It was somewhat of an epidemic, at least here in the States.

in, even as of 10 or 15 years ago, really sort of post FELV vaccine, that number dropped to about 15% and it's continuing to go down. So that's actually obviously a wonderful thing, . And again, if you sort of flip those numbers around, it actually looks like if you're an FELV positive CAT, you have about a 1 in 4 chance of actually coming down with lymphoma.

So it's actually quite, quite high risk. And again, if you flip that around, yet a third way, you could actually restate that to say that if you're an FELB positive cat, your risk of lymphoma is 62 times higher than if your FELB negative. And if you're, have FIV that risk is about 6-fold increase.

And if you're double positive, That risk is further enhanced. So, even in this day and age, we do really strongly recommend that all the cats, at least over here, get tested for FELD and FIV partly because, it's a husbandry issue, right? So if you come from a cat household with multiple cats and one of the cats has it, you certainly would want to get the rest of your cats tested.

There may The other issues if your cat is an indoor or outdoor cat and test positive for FELV FIV, you may want to change that and keep that cat indoors, so you're not spreading it around to other cats. And finally, actually, FELV positive cats have a worse outcome with therapy, so it also has prognostic importance. So for all those reasons, sort of having that information remains important even to this day.

So, how's a cat with lymphoma likely to show up at your practise? Obviously, this is gonna be incredibly variable depending on the part of the body, which the lymphoma, affects, and we can see a, a quite large variety of anatomic sites of lymphoma. The most common these days is the alimentary form, but we can also see multicentric lymphoma that, that actually resembles quite a bit the dog form.

We can see primary medias sinal lymphoma, we can see primary renal lymphoma, we can see primary nasal lymphoma, etc. And obviously, the signs that we're gonna see are really Related to where the lymphoma is manifesting. But the most common form that we're gonna see again is the elementary, followed closely behind by the mediastinal and multicentric forms.

And most of these cats are actually going to present, with the typical signs that every sick cat experiences, irrespective of the disease that they have, loss of appetite, vomiting, hiding, weight loss, etc. Etc. And then again, the other signs that you can see, again, are, are exactly related to the, the manifestation of the lymphoma.

Again, lymphoma is a disease of white blood cells and as a result, it has access to all the different parts of the body. So theoretically, we really can see lymphoma occur anywhere. So really, it could be on your differential list for just about anything, in a cat.

But again, the GI form of the disease is the most common one that we see. And again, in, in cats, this is a change from the, from the pre-FELV vaccine era. So in the pre-FELV vaccine era, actually the most common form that we saw was the mediastinal form, and that generally occurred in young cats.

Post-FELV, again, this is generally an old cat disease. They're generally FELV negative, and again, it's the elementary tract that tends to be most commonly affected. You know, loss, loss of appetite, lethargy, vomiting, diarrhoea, again, hiding, sort of behaviour change, etc.

There may or may not be blood in the vomit or in the stool, as well. So that doesn't really help us rule in or rule out lymphoma either. So, just a, a quick note, this applies equally to both dogs and cats.

Lymphoma is obviously not the only disease where we can see some degree of lymphadenopathy. So whether it's peripheral lymphadenopathy. Whether it's abdominal lymphadenopathy, just because we see that doesn't, doesn't guarantee that the disease that we're treating is lymphoma.

So obviously, we can see lymph nodes become enlarged anywhere in the body, as a result of a variety of different kinds of reactive conditions. Any kind of inflammatory condition can cause some amount of lymph node reactivity. Certainly, depending on where in the world or where in the, in the United States we're practising, we do think about mycotic disease, so fungal disease as being a cause of lymphadenopathy as well.

I've seen, seen some cats with very severe skin disease that can have actually quite pronounced peripheral lymphadenopathy, and then other immune-mediated diseases as well can sometimes cause generalised lymphadenopathy. And the reason that, that I think it's sort of worth remembering this is that We really try very hard to impress upon folks, to avoid, sort of empiric treatment with corticosteroids. For animals with undiagnosed lymphadenopathy, whether they be cats or whether they be dogs.

And really, there's two reasons for that, that, that pertain to the lymphoma specifically. So one is, sometimes corticosteroids can have enough of an anti-neoplastic effect by themselves that they can actually mask. Lymphoma and actually make it quite hard to, then sort of pursue subsequent diagnostics.

The other thing that they can do is actually make the lymphoma cells look very strange. So sometimes the pathologist may have a harder time than usual making a call of lymphoma, if those cells have actually seen corticosteroids. And then the second reason is, and this is much better described in the dog literature than the cat literature is at least in dogs, significant amounts of corticosteroid exposure prior to the initiation of chemotherapy is actually associated with a much worse outcome.

So it appears that, corticosteroid pre-treatment has the ability to actually induce varying degrees of chemotherapy resistance. So if we have an owner who would do more than just corticosteroids if a diagnosis of lymphoma is made, we really want to avoid these steroids whenever possible, to not screw up our diagnosis and again, to maximise the chance of a good response to chemotherapy. So, do we need a biopsy for every dog or every cat with lymphoma?

The answer there is no, really, we don't. There's quite a few of these that can be diagnosed, sufficiently with cytology. And again, these are generally not, we'll get into this distinction in a bit.

So these are generally not our low grade small cell lymphomas. Those can be incredibly challenging to diagnose cytologically, but our intermediate to large cell, intermediate to high grade lymphomas. That we certainly can see in cats.

We often can diagnose cytologically. This is kind of a, a, a classical appearance for, for a larger intermediate cell lymphoma. So it's a pretty monomorphic or, or a monotonous population of these large round cells, and I'll give you a little closer up view here.

So again, so really these cells are, are distinct from each other, so they're not clumping, they're not sheeting, they're quite round, they're not spindly, they're not oblong or elongated. They, these cells obviously have very high nuclear cytoplasmic ratios, but one of the questions that a lot of, a lot of people have, and one of the questions that my students have often is, well, I'm, I'm looking at the the cytology slide, how can I tell if the cells that are down there are large or not? So there's actually two very nice yardsticks that you can find on most, cytology slides like this that you can actually use as a gauge for whether the, the, the round cells that are seen are actually large or not.

So one of them is a red blood cell. So the diameter of a red blood cell is about the same size as the nucleus of a normal small lymphocyte. So in this field, you can actually see that the nuclei of most of these cells are considerably larger than the red blood cells that you can see in the field.

The other is a neutrophil. And again, you can see 3 or 4 neutrophils kind of floating around in this particular field. So the diameter of a regular small lymphocyte is around the same as the diameter of a neutrophil.

So the entire lymphocyte is about the same as a neutrophil. And again, in this field, you can see that the vast majority of these lymphocytes are considerably bigger than that neutrophil. So again, these certainly would be considered with, with intermediate or large sized.

Mononuclear cells, which again would really be supportive of a diagnosis of lymphoma if every field that you looked at had cells that looked like this. So there are some situations where really sites or, or histopathology can be very important and this is more often seen in cats actually than in dogs. So, one is in cats with peripheral lymphadenopathy, especially sort of younger cats.

One of the reasons for that is that there are, there are certain kinds of sort of weird hyperplastic lymphoid conditions that that some younger cats can develop with peripheral lymphadenopathy that can sometimes sort of mimic neoplasia by cytology alone or they can be sort of equivocal. And the other is there's this, a condition that's somewhat uncommon but seen called a Hodgkin's lymphoma or Hodgkin's-like lymphoma, which often presents with peripheral lymphadenopathy, often in the cervical region and actually can have a fairly indolent course. So this is unequivocally lymphoma.

It can be challenging to diagnose cytologically. But, it's a really important distinction to make. And this is just a quick picture of kind of what that looks like.

There are these classic. Little cells that you can see here called Reed-Sternberg cells. So these little guys are actually not the lymphoma cells themselves.

These are actually activated macrophages which are, which are present, which, which confer what they call this sort of starry sky appearance. And this is really something that's, that's not seen in dogs with any frequency, but occasionally in cats and more commonly in humans. But again, the reason that this distinction is important is a fair number of these cats can have actually a very, very indolent course of, of treatment or, or, or disease progression.

And as a result, they can be treated with, for example, if they only have localised surgical cervical lymphadenopathy. They may be able to be treated with surgery alone, just remove those lymph nodes. Local radiation therapy can be very useful.

And again, when those kinds of treatments are employed, these diseases can often progress very, very slowly, and it's quite common for the average cat to do well for more than a year with local therapy alone. So, nice thing to keep in the back of our heads again, for a cat with peripheral lymphadenopathy, especially in the cervical region, that seems to be progressing relatively slowly. Think about this Hodgkin's-like lymphoma.

The other situation in which, in which I really think that, that it's pretty important to do, to do histopathology is for the gastrointestinal form of the disease. So one of the reasons obviously is there are a lot of other sort of infiltrative gastrointestinal diseases that kitty cats can get that'll have a very similar clinical presentation and actually a similar ultrasonographic appearance. So, inflammatory bowel disease, diffuse mass cell disease, etc.

Can have a very sim similar appearance. So, the appearance of an ultrasound is not sufficient to make that diagnosis. And then the other thing is that, as we'll talk more about from a therapeutic perspective, there are really two quite distinct, clinical entities of gastrointestinal lymphoma that we can see in cats.

We have the low-grade small cell variety of the disease, and we have the intermediate to high grade. Intermediate to large cell variety. And the differences are, are vast both in terms of how we treat these and their potential outcomes.

So really having an understanding of which is which is quite important actually. And that generally requires histopathology. If one can make a diagnosis of lymphoma based on cytology, for example, of a lymph node, by definition, all Most, that's going to be intermediate or high grade.

Because again, in a low grade form of lymphoma, all the cells that you're gonna pull out of there are gonna be normal-looking small lymphocytes. And usually cytologically, that's gonna be a conundrum for your pathologist. So again, if, if your pathologist can make a diagnosis of lymphoma from a fine needle aspirate, it is almost never low grade.

So that's an important thing to consider. So, we talk a lot about staging. When we talk about canine lymphoma, there's this 1 through 5 staging schema, with substage, depending on how they're feeling, etc.

Really, this staging system is not particularly useful in cats, from a prognostic standpoint, and the large majority of cats that we see, actually do come in with clinical signs of illness versus being sort of the asymptomatic animal with, with just enlarged lymph nodes. So most are substage B. And again, the staging system really just doesn't, doesn't usually give us any additional information.

So, And if we're gonna be very complete in, in the quote unquote workup, whether you call it staging or whether you call it workup for a cat with lymphoma, these are generally the things that we'll think about doing. So, obviously, your basic sort of health screen, blood work-related stuff, do they have the appropriate number of like blood cells and other cells? Are their organs working the way they're supposed to?

So these are general general health kinds of constraints. That are really important to let us know about fitness for chemotherapy as well as the presence or absence of any other old animal diseases that might sort of modify the owner's interest in treating the lymphoma. Chest X-rays can be very helpful and obviously maybe a primary modality of, of diagnosis if we have an animal that presents with respiratory signs or, or evidence of a pleural effusion.

Abdominal imaging, again, especially in these animals who present with GI signs, we actually find ultrasound to be far more, informative, than flat radiographs are. Bone marrow aspirate, really the only situation in these days in which we'll consider doing bone marrow aspirates is if we have an animal that presents with, cytopeniaas where we're significantly concerned about bone marrow infiltration, or again, if we have a cat where that's the only presented complaint is weird cytopenias. And as I mentioned before, we definitely want to look at FELVFIV status.

And then immuno phenotyping. Again, it's something that we do more routinely in dogs than we do in cats, because it has quite a bit more prognostic significance. But I will spend a bit of time just talking about immuno phenotyping.

So there are a number of different ways that actually this can be performed. And again, what I mean by immuno phenotyping is again, determining the cell of origin of these lymphomas. And again, in, in very broad characteristics, we can subdivide lymphomas into those that arise from T cells and those that arise from B cells.

We're getting much better at at subcharacterizing lymphomas in dogs based on the expression of a variety of other markers on the cell surface. And again, this is a more advanced in in dogs and carries more prognostic significance in dogs. But, since time immemorial, the gold standard has been immunohistochemistry.

So this is actually applying special stains to biopsy samples that are obtained. 11 of the things that we're seeing an increase in, at least here in the states, is the use of immunocytic chemistry, which is actually applying these same stains to fine needle aspirates that are obtained. And obviously, there's a lot of advantages to this in terms of cost and morbidity to the patient.

If you can actually get this information from a fine needle aspirate versus versus requiring a biopsy. There's a technique called flow cytometry that's actually becoming much more ubiquitous both in the US and in the EU these days. So there's several places around the US that have this capability, and I know there's some expertise in flow cytometry in the EU as well.

So this does require live fresh cells that are generally need to be sent overnight. To the laboratory that's gonna do the test. And then finally, there's a test called PCR for antigen receptor rearrangement or PAR, which is actually a technique that looks at the DNA of these lymphocytes.

And, and we'll talk a little bit more about each of these. So again, immunohistochemistry is really thought of as the gold standard. It's been around the longest period of time and it's quite reliable.

And again, immunocytic chemistry actually is a technique that utilises these exact same stains, but can actually apply them to fine needle aspirates instead of to biopsy samples. Flow cytometry is a test. That actually uses very similar antibodies, similar special stains, but instead of being applied to tissues or to slides, actually cell suspensions are incubated with these antibodies or similar antibodies.

And then instead of using sort of the more common histochemical stains that would result in a red colour, or a brown colour, these antibodies are generally conjugated to flurochrome. So these are conjugated to fluorescent molecules. And then essentially what happens is, the single-cell suspension is sucked up into a special machine that illuminates the individual cells with different wavelengths of light.

And how brightly these individual cells glow is an indication of how many of these little antibodies are stuck to their surface. And as a result, you can actually get information about, are there T cell markers, T cell-specific antibodies that are stuck to these cells? Are there B cellspecific antibodies stuck to these cells, as well as a variety of other markers.

It can be quite useful for the characterization of lymphocytosis. So if you have an animal that presents with a, with a high circulating lymphocyte count, this test can be quite useful to determine if all those lymphocytes sort of have the same phenotype, which would be more indicative of a neoplastic condition. It can often be useful for trying to determine whether, again, a group of atypical cells in the blood is originating from a lymphoid or a myeloid lineage.

And again, at least in dogs, there's a subset of dogs with leukemias that actually have expression of a, of a primitive marker called CD34 which is associated with a, a quite dismal outcome and that's additional important information. It can also be quite useful for distinguishing between mediastinal lymphoma and thymoma, which can be sometimes a tricky undertaking both in cats and in dogs, because both of them actually contain lymphocytes. And in some cases, the, the appearance of the lymphocytes can be different, but this can sometimes actually be sort of a diagnostic dilemma, cytologically, and again, flow can be very helpful for that.

I'm just gonna stick this, skip this because it's mostly what we talked about already. And then the final test that, that, we'll sometimes use both in dogs and cats is this test called PCR for antigen receptor rearrangement. And again, this is a DNA test that actually looks very specifically at at the T-cell or B cell receptors.

And if we sort of, go back into, into ancient history and remember our vet school immunology lectures, one of the things that, that we can remember is that The way that immune systems sort of have evolved in order to be able to recognise a vast array of different antigens, be they B cells or, or be they T cells, is through a whole bunch of sort of reshuffling of genes that occurred during B cell and T-cell development. And again, you may remember the term VDJ recombination as the way that these genes get shuffled around. And they get shuffled around in such a way that, again, there's an enormous diversity of, of receptors that are present on the surface of these cells that allow the immune system to recognise all these different pathogens.

But one of the things that's really interesting is when that happens, actually, the size of the product that, that these cells end up with is actually very, very different from cell to cell. And you can take advantage of that. Sort of piece of information to actually design, tests, to, to look at whether each individual cell in a sample started from the same clone, or whether they started from a different clone.

So again, here's this thing that I, that I was trying to explain about the VDJ recombination that actually happens. And the fact that, within a B cell, and again, the same thing is true for T cells, the gene that you end up with can actually be variable in size. And that actually forms the basis for this test result.

So this is a test that's done with DNA and as a result, it doesn't have to be live. It doesn't require live cells. It can be done through using a whole bunch of different kinds of biofluids.

So it can be done using tumour tissue, it can be done using blood, it can be done using, we've occasionally done it from bone marrow, we've done it from aqueous humour. We've done it from cerebrospinal fluid. .

It can be done on on slides that have already been stained, which is also a really useful thing. So you don't necessarily have to get the cat back, reaspirate it, or anything else like that. Some labs will be able to do this assay from formalain fixed paraffin embedded tissues, some will not.

Our particular lab, doesn't, doesn't do this, the sample on formalin fixed tissues, unfortunately. But here's essentially what you'll see at the end of this test. So if you have a sample that is comprised of a variety of lymphocytes that started from different lineages, which again would be more indicative of a reactive process.

You're gonna see a variety of different sized PCR products. So sort of a smear or a ladder of different sized PCR products, suggesting, yup, you know, every time we sort of did this test, there's a whole bunch of different cells and each cell has a different sized VDJ region. That's kind of what this is gonna look like.

And generally what we see is one set of primers that are for T cell, one set of PCR primers that are for B cell. You have a neoplastic condition. Again, in, in theory, every single cell in that sample probably started from the same lymphocyte.

And as a result, you're much more likely to have a single, very, very bright band, which again would be indicative that every single cell in that sample has exactly the same BDJ region. Again, so that's an indication of a neoplastic condition. So you really get two useful pieces of information from this.

So one is, is the sample neoplastic or not? So it can be used as a tiebreaker in the case of equivocal cytology or even equivocal histopathology. And again, you do get information about T cell versus B cell as well.

The test is, not quite as sensitive, in cats as it is in dogs. So in dogs, it's about 85 to 90% sensitive. In cats, it's about 70% sensitive, and the specificity is unknown.

So again, I think, the, the two situations in which we still consider this to be quite a useful test are in those situations where we may have a questionable biopsy of, for example, an intestinal lymphoma. I think we've all been faced with a situation perhaps where we do either a full thickness biopsy or endoscopic biopsies and the pathologist come back and say, well, it might be lymphoma, it might be really bad IBD we really can't say for sure. So this can be a very useful tiebreaker in that kind of situation.

And just like in the dogs, it can also be useful for making that distinction between lymphoma and thymoma. So again, what our, internal medicine folks will often do when they're doing an endoscopy in a, in a kitty cat is actually get some extra biopsies of the intestinal tissue and freeze them. So that if we do end up with one of these equivocal, histopathological diagnosis, there's a sample that's been saved that's actually suitable for, PCR for antigen receptor rearrangement, which again, at least in our lab can't be done, on a paraffin section.

So another test that you may have heard of, is a test called thyidine kinase. And this is actually something that's been looked at quite a bit more in dogs than in cats. So thymine kinase is an enzyme that's very important for DNA replication or cellular replication.

And for reasons that aren't entirely clear for in certain kinds of cancer and the one that's been the best studies is lymphoma, this enzyme tends to leak out into the bloodstream and can actually be detectable in, in serum, from, animals with lymphoma. And again, this has been looked at very nicely in Sweden. And again, dogs with lymphoma have much higher TK levels than dogs with other diseases, and there's a correlation actually between how high TK is and the stage of disease, as well as substage.

So dogs with substage B disease are more likely to have high TK than dogs with substage A disease. So, it, it's an interesting test. It's not 100% accurate by any means, and there certainly are other neoplastic conditions that Sometimes be associated with high TK, for example, hemangiosarcoma in dogs.

This has also been looked at in cats. So again, from the, actually a number of individuals around the world sort of contributed to this study. And yes, in fact, TK does appear to be higher in cats with lymphoma, that's the L samples here than in normal cats, in cats with inflammatory diseases or in cats with other kinds of neoplasia.

But as you can see, there's actually quite a bit of overlap between these conditions. So again, there's quite a few cats with lymphoma who had normal TKs. There's a few cats who had inflammatory diseases or other kinds of neoplasia, who had quite elevated TK's as well.

So, unfortunately, it's really not sensitive or specific enough to be what we would consider to be a definitive test for lymphoma. And again, one of the other big problems is that as I mentioned earlier, it's really critical, especially in these cats with the GI form of the disease to make a distinction. Between the intermediate or high grade form of the disease and the low grade form of the disease.

And unfortunately, this test does not allow that. Oh, let's talk about treatment a bit. So, one of the things obviously that, that is a very reasonable treatment for owners who want to be conservative is corticosteroids alone.

And quite a few cats are gonna improve with corticosteroids, more than half at least are gonna have clinical improvement. For cats with the intermediate or high grade form of the disease, we probably expect corticosteroids alone to, to have some amount of clinical benefit for something like 1 to 2 months. So is it better than not doing anything?

Absolutely. It, it unequivocally is. Certainly not as good as some of the other things that we have to offer.

And corticosteroids alone may be more useful than that in cats with the low grade form of GI lymphoma, but again, we don't have any statistics looking at the effectiveness of corticosteroids alone in those particular cats. For a very long period of time, COP, the cyclophosphamide vincristine and prednisone, has been a really acceptable treatment of this disease in cats and, and what we consider to be a good middle of the road, kind of protocol. And again, when we're talking specifically about cats with, with intermediate to high grade lymphoma, the likelihood of seeing a complete response is about 50% and the average remission duration is generally in the neighbourhood of 3 or 4 months.

Oh, considerably better than prednisone alone. Perhaps not as good as some of the other tools that we have in our toolbox. Eric Tesa from UTrek actually published a very interesting paper a few years ago showing that, actually the cop drugs, the vincristine and the cyclophosphamide that are used as part of the COP protocol can actually be given intraperitoneally in cats, and it's actually quite well tolerated.

And again, especially if you've got a cat who's not particularly nice, where venous access could be an issue, this actually does appear to be, to be quite a legitimate alternate route of administration of these drugs. our group here actually recently took a look at whether, whether oral and intravenous cyclophosphamide appear to have equivalent, drug exposures when given. And, at least in normal laboratory cats, the answer does appear to be yes.

So, here in the United States, at least, intravenous or injectable cyclophosphamide has really become prohibitively expensive. And as a result, for financial reasons, many of our owners have had to resort to the oral form. And again, I think we can look at an owner and say, yeah, based on the pharmacokinetic analysis, it does appear in cats and actually in dogs as well that that they're interchangeable as far as how much actually gets into the bloodstream and how much the lymphoma cells see.

One of the pieces of information that's actually quite nice that, that we determined recently or was determined recently in the, in the profession is that, cats seem more likely to have some amount of gastrointestinal disturbance from vincristine than dogs do. So, we do know that that agents like Bencristine can be associated with hypomotility, so they can actually interfere with gut motility. And some cats can develop some gastrointestinal signs, loss of appetite, nausea, constipation, etc.

As a result of vincristine. A group at University of Pennsylvania actually recently did a study comparing the incidence of gastrointestinal effects from vincristine or viblastine and actually whether there was a difference in outcome between the two groups. And on the plus side, actually both of them were plus side, so there was no difference in outcome.

Between the cats with crystine and the cats with blastine, and the cats with blastine actually had significantly less gastrointestinal disturbance. So here, we generally tend to start with vincristine anyway because it's in the majority of cats, it's tolerated just fine. But if we do see a cat who has a problem with vincristine, we do feel like we can make the switch to blastine, you know, without any, any impact on outcome, which is very nice to know.

So really the gold standard for the treatment of cats with, with most forms of lymphoma, these intermediate or high grades of lymphoma remains a CHop-based chemotherapy protocol. So you take the COP protocol and you add the drug doxorubicin. And again, there are a large number of different sort of iterations of this COP protocol that have been published in the literature both for dogs and for cats.

One of the more common ones that people may have heard of is what's called the UW Madison protocol. There's a cat version and there's a dog version. But, all of there again are several of these that all sort of use the same drugs and just sort of mix them up into different orders or maybe continue them for different periods of time.

This is just one of the, the papers that actually comes from Hanover, that looks at this in cats with intermediate to high grade lymphoma. And again, looking at about a 70% response rate in these cats to a chop-based protocol. Almost half of those responses are complete responses, where again, you're looking at an average response duration of about a year, so not too bad.

And then about a about a quarter of cats will experience a partial response, and the average duration of that partial response is a couple of months, generally. So the number one predictor of outcome in these cats, unfortunately is response to therapy, which is something that we can't. Assess a priori.

So the only way you know about response to therapy is to treat them and see how they go. But again, if you take all these cats and put them together, you're looking at median survival times probably in the 6 month range or so. And again, if you have a cat who experiences a complete response, it may be significantly longer than that.

So this really remains our gold standard, if the owner is willing to do it. One of the things that those of us who are familiar with the treatment of lymphoma and dogs may, may think about is one of the middle of the road, quote unquote protocols that we quite often will offer in dogs whose owners want to do something beyond corticosteroids alone, but may not sort of have the wherewithal to do a completech protocol as single agent doxorubicin. And this is, you know, quite a nice middle of the road protocol in dogs, but there are actually a couple of studies in cats that really suggest that single agent doxorubicin is not particularly effective for them.

So it is not generally the protocol that we'll reach for, for an, for an owner who wants a middle of the road cat lymphoma protocol. The other thing I'll mention about doxorubicin in cats is, unlike in dogs, the, the dose limiting cumulative, adverse effect from doxorubicin in cats is actually azotemia. It generally does not cause clinically relevant cardiotoxicity, but it does cause azotemia.

So we would not give doxorubicin to an azotemic cat. And generally, as we're moving along with therapy, whether we're using doxorubicin as a single agent or integrated into a CO protocol, we generally will, routinely check renal values before each dose of doxorubicin to make sure that a cat isn't becoming azotemic as a result of our therapy, in which case we would want to stop the doxorubicin and potentially swap it out for something like midazantro. Oh, a very, very interesting study that, that was published quite recently actually, has, has given us another option, sort of middle of the road option for the treatment of cats with lymphoma, and that's Lomustine.

So Lomustine is really nice because it's oral, and again, it's actually quite, a non-intensive. So in the average cat, this is a single pill that's administered every 3 to 5 weeks, with or without prednisone, with or without, an injection of asparaggenase at the same time. So, if we're looking for a middle of the road protocol with intermediate efficacy, and we're comparing sort of the old tried and true cop protocol to a protocol like low mustine, you know, I certainly come down in favour of low mustine just due to its simplicity, the infrequency of administration, and certainly it's, it's really high tolerability as well.

So you can see the numbers here. Overall response rates are about 50%, the likelihood of a complete response is about 25%. So, again, it's certainly not as efficacious as Chop, but it really does sort of fall into the same range as what we would see with the COP protocol.

And again, it's quite simple. So, again, if we have an owner who wants to do something beyond prednisone. But it's probably not, not really geared up for a full chop protocol.

I really think that, that, that lousine plus or minus a little bit of asparaginase at the beginning, can be a really, a really reasonable sort of middle of the road approach to taking these cats. So what about, we talked about rescue therapy a lot in dogs. So we do know that eventually virtually all cats and dogs with lymphoma are going to relapse.

And actually, the information that we have about rescue therapy for cats with with lymphoma is considerably less. Robust than what we know about in dogs. So if, for example, we had a cat that started out with a chop type of approach, or a cop type of approach, certainly one of the things that I would be high on my list to try would be Lomaine plus or minus asparaggenase.

There's some information using other injectable multi-agent protocols. Again, a couple of those are listed here, MOP and DMAC as options. One of the things that's quite interesting is a, is a small pilot study that was done looking at, at whole abdomen radiation therapy for cats with refractory gastrointestinal lymphoma.

And again, this is a very small study. Only about a dozen cats, but these cats just got two quick doses of radiation. These are again, shined down to the whole abdomen.

It doesn't require any fancy advanced imaging to plan or anything else like that. And actually, there was clinical improvement in 10 out of the 11 cats that were treated in this study. And again, the average cat did well for about 7 months after this treatment was received.

So really, and, and it was quite well tolerated. So, again, very, very preliminary. I'd love to see this repeated.

And have more information to be able to quote to owners, but I really do think that if, if one is practising in an area where, where radiation therapy is feasible, you know, within a reasonable drive, this definitely is something that could be considered as a, as a rescue or salvage therapy if, chemotherapy is sort of worked for a while and then stopped working. And again, there certainly are some people who are looking at, at ways to potentially integrate chemotherapy and radiation. So rather than using it as a rescue therapy, can we use it sort of to, to potentially after chemotherapy immediately to try and increase response duration.

And again, that's a, that's a work in progress as well. So, one of the things that owners obviously are very concerned about and that we have to do some, some dispelling of myths with, with owners is the concept of quality of life. And, you know, many owners are gonna have a personal experience with chemotherapy with themselves or family members or friends, and they'd say, oh my God, I, I would never do that to my animal, you know, my, my great aunt Harriet was in and out of the hospital all the time.

And she felt miserable all the time and those kinds of things. And again, obviously a lot of owners are gonna anthropomorphize with their pets. And one of the things that we as oncologists actually spend a lot of time doing is really trying to sort of dispel the myths of chemotherapy in animals.

So again, despite the fact that for the most part, the drugs that we are using are are human cancer drugs, the way that we give them is actually quite different, both in terms of the doses that, that would be given even to a similarly sized patients. And again, in humans, they'll often give sort of all the drugs at the same time. We tend to give them one at a time instead.

And again, having that, that discussion with an owner to help them understand the, the similarities and differences between chemotherapy and in animals and in people can really help an owner to understand that the goal behind these treatments is really to preserve quality of life, and to make it so these animals can just get on about their business rather than Something that is going to negatively impact their quality of life. And again, so the, the top study here is a JSAP study that actually looked at dogs and 92% of owners were actually quite satisfied with the with the outcome from their lymphoma treatment. a second, paper that came out in the Journal feline medicine and Surgery actually took a look at cats receiving chemotherapy.

And again, the average quality of life score in cats that receive chemotherapy almost doubled. From before chemotherapy to after chemotherapy. And again, the vast majority of owners were actually quite happy that they treated, and would be happy to treat again.

So again, this information again, I think is quite useful for owners to say, look, our goal is not to negatively impact the quality of life of your cat. It's actually to significantly improve it, and I think we're pretty successful at being able to do that. Again, a word about low grade lymphoma.

So there's actually now quite a few studies. I think I've listed 4 here, but there may be 1 or 2 additional ones that are actually specifically characterised this disease. And again, this is a disease process that cannot be diagnosed cytologically.

It does require histopathology. And again, the big reason why we think that making this distinction is so critical is because these cats can actually have quite a good outcome with a very conservative form of chemotherapy. So generally, the treatment that we recommend for these cats is a combination of two pills.

One of them is prednisolone and the other is chlorambuil. And there are a couple of different ways that this chlorambuil can be administered. The very first one that was reported is the protocol that you see here, the 15 milligrammes per metre squared, 4 days in a row, repeated every 3 weeks.

There's a second group that's actually reported on 20 milligrammes per metre squared all at once, just every other week. And a third way is what we call sort of the low dose continuous method of treatment, which would be a single 2 milligramme pill per cat every 2 to 3 days. And again, is it 2 days, is it 3 days?

It kind of depends on the size of your patient and that's kind of an inexact science. Generally, all three of these are actually incredibly well tolerated. We see very, very little in the way of adverse effects from this treatment.

And the outcome is actually quite good. So about 85% of cats will respond symptomatically. And again, depending on the study that you pick up, the average survival times are in the neighbourhood of 18 to 24 months, with treatment.

In one paper, those cats who eventually relapsed were successfully retreated just by switching to a different oral chemotherapy drug. So those cats that failed chlorambuil could, could be adequately rescued just by switching to cyclophosphamide, another oral chemotherapy medication. So, yeah, really, again, a critical distinction to make because these cats can do so, so well.

And again, if you ask the opposite question, what happens if I use prednisone or chlorambucil in a cat with intermediate or high grade lymphoma? That's like spitting in the wind. It's really gonna be no difference probably than if you just use prednisolone by itself.

So again, making this distinction is really critical. And again, very recently, there's been sort of additional work tried, tried to be done from Matty Coopple's group, who's a pathologist at, at Michigan State University, to find better ways to make a distinction between sort of severe inflammatory bowel disease and low grade lymphoma. And actually what his lab has determined is that a combination of histopathology.

Immuno phenotype, and clonality assessment with the PCR based test that I mentioned, is the most reliable way to make that distinction in the case where there is any kind of vagueness. So if the pathologist does come back and say, I can't really say for sure which one it is, that's where I mean a phenotype can actually be very, very useful as well as clonality testing. And again, there are multiple, multiple studies that have demonstrated unequivocally that full thickness biopsies are superior to endoscopically collected biopsies for making this diagnosis of GI lymphoma versus IBD.

So again, it is more invasive, it probably is more costly. But it is something that everybody can do in practise. You know, most people in practise can do an exploratory laparotomy.

Not everybody in practise can do endoscopy. And again, the big reason why it's so much more useful is the size and the thickness of the biopsies that are obtained. So, the samples that you get are much better from a full thickness biopsy than they are from these little tiny endoscopic tweezer-like biopsies that we can receive.

So whenever possible, this is actually what we recommend, sort of go back to the old school, and actually do the X lap to collect your samples. Very quickly, I think Sue's gonna mention a bit more about nasal lymphoma, but we certainly can see cats with nasal lymphoma. And the big difference between nasal lymphoma and most of the other forms of lymphoma that we see in cats is nasal lymphoma is usually solitary at the time that it presents.

So we're always very thorough about looking for evidence of disease elsewhere, but it's usually not there. And as a result, local treatment can actually often be quite effective. So one study that looked at a, a combination of radiation therapy and chemotherapy, reported, reported a median survival time of almost 3 years with that combination.

And a larger study actually looked at a variety of different treatments, including, radiation and chemotherapy, radiation alone, chemotherapy alone. All were fairly efficacious. But actually, in this particular study, there was no statistical difference between cats who got radiation by itself and cats who got radiation and chemotherapy simultaneously.

In fact, the radiation alone cats numerically did better. So, in our practise, generally, whenever possible, we would opt for the radiation therapy option. And we keep our chemotherapy in our kind of in our back pocket for use later on down the road if, if relapse is noted versus sort of blowing both of them up upfront when there may not be an advantage to that.

Certainly, if we're again in a situation where radiation therapy is simply not possible. Due to location, sort of geographic location, due to owner finances, anaesthesia risks, etc. Chemotherapy alone is certainly a very, very reasonable outcome and, and the, the, the outcome in these patients does seem to be better than your average lymphoma of other sites.

Heinous lymphoma is quite rare in cats, but just like in dogs, it certainly can be seen and can have quite a wide variety of clinical presentations. And this is a disease that that really has not been studied adequately in cats for us to be able to make any strong recommendations about treatment modalities or or outcome. So, generally, again, Sue's gonna give a whole lecture saying that cats are not small dogs, but this is one situation where I think we're, we're sort of forced to sort of treat cats like small dogs because we simply don't have the information about outcome in cats.

With one exception, and this is one particular form of, of cutaneous lymphoma that we can see that actually occurs around the tarsus in cats, which is a very odd clinical presentation. This is generally considered to be a non-epitheliotropic lymphoma. Most of them are large cell.

And again, it looks like the median survival time is around 180 days if you take everyone and put them together. Only about a quarter of these cats have disease that extends beyond the tarsus at the time of presentation. And the limited information that's actually depicted in that little Kaplan Meyer plot in the upper left corner there does suggest that cats that are treated with a combination of local therapy, either surgery or or radiation therapy and chemo tend to have a better outcome than cats that are treated with medical therapy alone.

So this is one kind of oddball presentation that at least we have a little bit of information about. I'm gonna skip talking about large granular lymphoma, other than to say it's rare and it's generally quite bad, quite bad. So again, you're looking at a, a median survival time in days of days to, to a month or two generally.

One very quick thing that I do want to mention here at the very end is a drug that some of you may have heard of and, and some of you, some folks in the UK have used. It's a drug called Taovia. So Tenovia is a drug that actually has what's called conditional approval here in the US for the treatment of canine lymphoma.

And this is based on actually quite a few studies that have been done looking at again, the use of this, this drug either as a first line therapy or as rescue therapy in dogs with lymphoma, with varying degrees of pre-treatment. Tanoia is actually a pro-drug that's converted to an active anti-metabolite called PMEG. The reason that a pro-drug strategy is used is that the PMEG itself is actually very, very, very toxic.

But this pro-drug strategy allows a relatively non-toxic compound to be administered that's turned into PMEG inside the tumour cells, and results in the, in the death of those tumour cells. And actually, it can work quite nicely in some dogs with lymphoma. So in the very first studies that were reported, about 80% of dogs actually had a response, and the majority of the responses that were observed were complete responses.

And again, when used as a rescue agent, it appears to actually be quite useful in a lot of dogs. There are no head to head studies comparing the efficacy of this agent with other agents, but numerically it does appear to be quite useful. And the reason that I do bring this up is that there is a feline dose finding study ongoing in the United States right now.

So, at least here in the US this is a drug that it would be a violation of federal law to use in a cat because of the, the quote unquote conditional approval that that it's currently operating under. But if and when this agent receives full approval in the US there will potentially be the opportunity for its off-label use legally in cats. And so we're certainly quite hopeful that by that time, we actually have what we think is a safe and efficacious dose in cats as well.

The approval status of Tannovia in the EU, you know, and or in the UK kind of depending on how things break out for you guys, at this point is unknown, and actually the, the ex-North America rights for Tannovia, are not held by the same company that actually holds the North American rights. So again, it's development status outside of North America, is not clear. Follow up, for these kitty cats, again, if we have something to image, that we know is enlarged, so whether it's enlarged lymph nodes, and mediastinal mass, etc.

We love it when we can objectively assess response in these cats versus going based purely on clinical signs. But certainly, often we are making assessments about outcome and whether we should continue doing what we're doing or something different based on clinical signs. So not ideal, but, but again, certainly is something that's an important component.

Of the way that we assess response. And again, one of the questions, especially for all of these lymphomas is how long do we treat? So for a very, very long period of time, our treatment, whether it was with an aggressive protocol like CHOP or whether it was something more conservative was indefinite.

So we would treat forever, although perhaps at a decreasing interval. More recently, at least with aggressive protocols like CHP, people have looked at, well, let's treat for 12 weeks or 16 weeks or 6 months and then stop. And and it appears that the outcome with these high grade lymphomas may be equivalent.

If treatment is discontinued after a period of time and then regular rechecks are, are employed in those cats that have a complete response. In cats with low grade intestinal lymphoma, really, the jury is out on how long to treat for. I'm a proponent of indefinite treatment as long as the, the drugs are tolerated.

There are certainly some other folks who will quit after 6 months or a year and then plan to restart treatment at the time of, of recurrence of clinical signs or lymphadenopathy. There are no comparisons of the two methods, and I think both, you know, are equally valid based on what we know and don't know currently. Oh, I know that was quite a quick little run through here and I do have a tendency to talk quite quickly.

I hope we do have just a couple of minutes to answer any questions that might be present, and again, I, I thank you all greatly for your attention. And again, I'd be happy to answer any questions at this point. Thank you very much, Doug.

A really thorough overview of feline lymphoma with some great information reviewing the literature on the current treatments, and I really, I thought it really helpful the way you considered the quality of life, because that's something that will really concern a lot of owners and of course vets who are perhaps are not specialists. So thank you very much for that. So we've got time for a couple of questions if anybody wants to put those in the Q&A.

Box, but we've got 2 here at the moment, and the first one is, why not use Vin blasting instead of Vin Christine from the outset? Oh, great question. So, so there's absolutely no reason not to do that.

I think most of us, especially sort of older, older oncology practitioners here, tend to gravitate towards V Christine because it's what we've been doing our entire careers. And again, in our hands, this is another thing that's really actually quite odd, is that there seems to be quite a bit of geographical variability that we observe with certain kinds of adverse effects with chemotherapy drugs in animals. So, at least across the United States, the, the folks in Philadelphia tend to see more intestinal upset from than Christine than we do.

In Colorado, folks on the east coast can give higher doses of low mustine to dogs than we can. It's very, very odd. So part of the reason is that again, I think many of us don't have quite the same experience with adverse GI effects from Vcristine.

And again, part of it is just because we're old-timers and, and this is the way we've been doing it all along, and the majority of cats tolerate it fine. But, again, in a practise situation, is there anything wrong with starting off, off the bat with bin blasting? Based on the, on the literature that we have, I, I think the answer to that is absolutely not.

There are roughly, at least in the states, roughly equivalent in cost. So I, I do think that's quite a reasonable substitution to make, in, in a practise situation. And again, I, I should, I should be more open-minded, and be willing to make these kinds of changes for myself as well.

Thank you for that. And while we're doing these questions, sir, if you want to start sharing your screen and getting ready for your presentation, we'll go straight on to you in a couple of moments. We've got a question here for you, Doug.

Can doxorubicin also be given intraperitone to cats? Ah, so that is an excellent question and that is something that has not been looked at. in general, we worry quite a bit more about doxorubicin.

As far as the damage to tissues in the region where it is injected than we do with most of the other agents. And as a result, I would be quite leery of giving doxorubicin intraperitoneally because of the damage it could do to the peritoneum. So that's one I think really, until someone has the, has the temerity to, to investigate it, I would consider, I, I would continue to give exclusively intravenously.

Thank you. Then we have a question here. What is the dose of Lomiine?

Ah, so that's another great question. And actually, in cats, there's quite a bit of different information about, about the dose that seems to be appropriate, but there are a couple of things that are different between cats and dogs. So one is, the dose that we recommend in cats is a bit lower than in dogs.

Generally, if you're dosing it on a milligramme per metre squared basis, most people will probably shoot for something in the neighbourhood of 30, sorry, 40 to 50 milligrammes per metre squared. But actually, one of the things Again, I don't know if this is the case in, in the UK but in the United States, one of the commercial capsule sizes that we're able to purchase is 10 milligrammes. That's actually the smallest capsule size that's made and actually in our hands, 10 milligrammes per cat.

Unless that cat is extremely small or extremely large, tends to be actually quite an acceptable and practical dose for most cats. The other thing that, that is important in cats is that we can see a, a higher number of cats than dogs actually develop a delayed neutropenia. So, yeah, they can get the one week mark, but there's quite a few cats, or even at the 3-week mark, we may see a, a, a degree of neutropenia that's often not dangerous for them, but low enough that it does make us not want to treat them again.

So, unlike dogs, there are some cats where we really need to adopt in every 4 or even sometimes every 5 week dosing interval to account for that delayed neutropenia. Hi, Doug, I don't know if you can hear me, but, we can't get the 10 milligramme, lousinet capsules in the United Kingdom. We have to get them reformatted.

So, but we do tend to get them reformatted into 10 milligrammes anyway because that's an easy size for people. So we do tend to still use 10 milligrammes per cat, but we have to get them reformatted. Got it.

So I think we'll call it a day with questions there so we can move on to our next presentation and keep the time. Thank you very much, Doug, for really fascinating and informative presentation.