Oral Chemotherapy in Cats: A Realistic Roadmap for Primary Care

In the June open access episode of Chattering With iCatCare, Yaiza Gómez-Mejías is joined by Mariana Lopes and Joanna Morris to explore feline oncology and the practical roadmap for using oral chemotherapy agents in general practice.  

The conversation focuses on providing realistic treatment options for patients where referral may not be accessible, highlighting how oral protocols can achieve efficacy and maintain quality of life within a primary care setting. They also discuss why cats must not be treated as small dogs regarding drug toxicity and the specific challenges of monitoring feline patients who often hide side effects.

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Oral chemotherapy agents in cats: clinical uses, administration and side effects

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Host:

Yaiza Gómez-Mejías, LdaVet MANZCVS (Medicine of Cats), RCVS CertAP (Feline Medicine), iCatCare Veterinary Community Co-ordinator

Speakers:

Mariana Lopes, DVM, MSc, MVM, MRCVS, DipECVIM-CA (Onc), European Specialist in Small Animal Oncology, University of Glasgow

Joanna Morris, BSc, BVSc, PhD, FRCVS, FHEA, DipECVIM-CA (Onc), Professor of Veterinary Oncology, University of Glasgow

Creators and Guests

Host

Yaiza Gomez-Mejias

Veterinary Community Co-ordinator @ International Cat Care

What is Chattering with iCatCare?

Welcome to Chattering With iCatCare, the official monthly podcast of International Cat Care, hosted by Yaiza Gomez-Mejias (Veterinary Community Co-ordinator). Each month, we chatter about cats and cat-friendly practices with industry experts and contributors to The Journal of Feline Medicine and Surgery. If you would like access to our members episodes become an iCatCare Veterinary Society Member and get in touch.

Yaiza Gomez Mejias: Welcome to another episode of Chattering with iCatCare. I'm Yaiza Gomez, iCatCare veterinary community coordinator, and today we are diving into feline oncology and oral chemotherapy. Joining us are Mariana Lopes and Joanna Morris from the University of Glasgow. They have published a clinical spotlight in the Journal of Feline Medicine and Surgery titled Oral Chemotherapy Agents in Cats - Clinical uses, administration and side effects. In this article, they review the most common malignancies we see in practice and provide a roadmap for using oral drugs.

Yaiza Gomez Mejias: I really enjoyed reading your article and I found that it's very useful and very realistic in terms of expectations and limitations around the use of these drugs.

Yaiza Gomez Mejias: Which are the most common situations in which vets should be thinking of oral chemotherapy and when should we not think about it at all?

Mariana Lopes: I think it just depends on the goals, doesn't it? There's probably always gonna be a situation where we could consider oral chemotherapy. That's the reason why we focus on oral chemotherapy on the article, is that sometimes not all patients will be able to have access to referral, be close to a referral facility, or will not be able to be referred for whatever reason.

Mariana Lopes: I think where the oral chemotherapy becomes useful is if we're trying to manage these patients into primary care practise, where potentially the equipment or the safety precautions will be a bit trickier with injectable chemotherapy, even if they're not getting the absolute best treatment that they could get if they were able to receive injectable chemotherapy.

Mariana Lopes: The oral chemotherapy becomes very helpful 'cause it's easier to administer, it's easier to source, easier to storage as well. I think there's lots of situations and lots of different diseases that we could consider oral chemotherapy, and lots of them will be very well treated and the treatment of a choice would be oral chemotherapy.

Mariana Lopes: We can think about things like low grade lymphoma in cats. It's very common, we diagnose very frequently here in the hospital that can very well be managed and very successfully managed with just oral chemotherapy. If we're thinking about more large cell high grade lymphoma, that's different. Ideally, we would want for best treatment outcomes to include some injectable drugs, but if that's not possible, oral lomustine can also potentially achieve some efficacy in these patients. That was kind of the point of the review. There's lots of different situations where you could do a lot of good for your patients just with oral drugs.

Mariana Lopes: It might not be the absolute best treatment out there, but it will still be better than nothing.

Joanna Morris: Providing you have a cooperative cat that will take tablets

Mariana Lopes: Exactly.

Yaiza Gomez Mejias: In the article, you noted that for certain drugs we might see less toxicity in cats compared to dogs with neutropenia frequently cited as the primary dose limited factor in feline patients. Why do cats tolerate these treatments differently and how should we monitor this feline specific risk?

Mariana Lopes: Cats are not just small dogs.

Mariana Lopes: Some drugs will be more toxic in cats, others will be less. Cyclophosphamide, commonly associated with hemorrhagic cystitis in dogs does not seem to have the same effect in cats. When we're treating a dog cyclophosphamide, we'll monitor the urine very carefully for microscopic hematuria, which is not as much as a concern in cats.

Mariana Lopes: Doxorubicin in dogs can cause cumulative cardiotoxicity. Temozolomide, which can be used in dogs with a variety of tumours, the main ones being brain tumours. It's not recommended in cats at all 'cause there isn't a safe dose. The times it has been trialed, it has proven to be toxic. It's very important to familiarise ourselves with the type of toxicity we might be seeing with the patients that we're treating.
Mariana Lopes: Because if some of that toxicity does occur, we would have to manage it. We would have to to treat our patients back to the whole quality of life aspect of things. We try as much as possible to not have our patients so sick that they need to be hospitalised for side effect management. But occasionally it does happen, and it's rare, thankfully, but sometimes we'll have to be aware of it so we can treat it effectively and also we can avoid it in the future.

Mariana Lopes: If we have a patient that has experienced toxicity with a drug and we're planning to use it again in the future, then we have to decide was the toxicity mild enough that we should do it again for the benefit that it's inducing to the disease? Was it so severe that we don't want our patient to experience the side effects again?

Mariana Lopes: Treatment changes will have to be implemented. Reducing the dose, increasing the intervals, replacing the drug with a different drug. All of those things are before just deciding, yes, let's do oral chemotherapy. Sometimes there is this misconception that just because it's a tablet, it will be fine, but it's not true.

Mariana Lopes: It's still chemotherapy. It should still be taken with caution. If we need to treat our patient, we need to treat our patient, but it's important to be familiarised with the possible side effects and being prepared to manage them if they occur.
Joanna Morris: With cats, because they're slightly more aloof, side effects are actually just not noted.

Joanna Morris: You may think the cat's not experiencing a lot of side effects, but it may be that it's just not being observed in the same way that a dog is. People are very aware of when their dog's urine and faeces change, or their interaction changes, but sometimes 'cause cats can keep themselves to themselves, it's harder to appreciate with a cat is actually feeling unwell.

Joanna Morris: You have to rely a lot on the owner's observation and reporting back to you to know whether it's actually undergoing side effects or not. Yeah.

Mariana Lopes: We're not even talking about the outdoor cats. They'll just do everything outside and sometimes we're asking how are things? And they're like, okay, couldn't tell you because I haven't seen anything.

Mariana Lopes: So we have to hope everything was okay and obviously if they're bright and happy and eating, that's a good sign. But sometimes there could be vomiting and diarrhoea happening that we just not aware of because it all happens outside.

Yaiza Gomez Mejias: When it comes to blood parameters, blood tests, have any general suggestions for a monitoring strategy when it comes to that neutropenia?

Mariana Lopes: Every single patient before receiving chemotherapy will have at least a haematology plus minus anything else if the drug has other organ specific toxicities, but a haematology would be the baseline for everything. So neutropenia, the most important thing is not giving chemotherapy to a patient that's severely neutropenic.

Mariana Lopes: That would be important because we would put them at higher risk of sepsis and acquired infections. That is the single most important thing. We also look at anaemia, thrombocytopenia, and things like that. Obviously all depends on baseline. If a patient is anaemic, but it's now less anaemic than it was two weeks ago, that's good.

Mariana Lopes: Anaemia on its own is not a contraindication. It has a lot to do with how things are progressing over time. If suddenly we've had a 20% PCV drop. Maybe we should go and look at why that's happening before we're just cracking on with the next dose. Same with the platelet count, but yes, neutropenia would be the most important thing.

Mariana Lopes: Then your cutoff. What's the cutoff? That is very variable, and I think it has a lot to do with how comfortable you are managing side effects if there were to occur, if you're not very comfortable at all or if you want to avoid them, you could use your normal reference range. Anything below the normal, delay a little bit and then give it once that's recovered. If you're more comfortable, you could accept a mild neutropenia. For cats, usually anything above two, we're quite happy, provided they're clinically well. If they're sick, we might prefer to delay, but if they're bright, happy non pyrexic and only mildly neutropenic that should be okay. Important to consider has the drop been very significant? Did our cat have a baseline neutrophil count of 10 and now after one dose of chemotherapy, it's now 2, perhaps we might not want to be as bold as we were the first time around. Maybe we could try a little dose reduction and see if we don't run into problems.

Mariana Lopes: And then if you don't, then you could go for a full dose next time. It's based on our overall clinical picture. We are not just looking at the bloods as an isolated piece of information. We're putting that into context with our patient, how well they are, how well they've been, their disease. Lots of patients will have diseases that will affect their haematology values, particularly patients with lymphomas or leukemias.

Mariana Lopes: So that's something to have into consideration. For example, patients with leukaemia, we will have to be a lot more permissive with their haematology values because if we're gonna wait for them to have a normal neutrophil count, we could be waiting a very long time or ever. So sometimes you just have to go ahead despite those low values. So yes, I think it would be very nice if you could have a blanket rule and say, just do this. Everything will be okay. It's not quite as simple as that. It all comes back to quality of life. If the quality of life is not good, let's hang fire. Let's give them some time to recover before we go again.

Mariana Lopes: That's the single most important thing. We want our patients to be happy at home, just having a normal life, and if that's not the case, then we have to change something.

Joanna Morris: If money is a real issue, I don't think you can actually cut corners with the blood test because that is an integral part of doing it safely. If the owners really do have financial issues, it may be better just to go for palliative care and not actually embark on the chemotherapy.

Joanna Morris: I think they've got to be engaged enough and have enough finances to do it properly. Otherwise, it's probably better to just advise something more palliative that doesn't require blood monitoring with blood samples.

Mariana Lopes: Just something, chemotherapy is the kind of thing that you can just do without being careful and without monitoring.

Mariana Lopes: Can you imagine that we're accidentally giving chemotherapy to a patient that's secretly very neutropenic? We're gonna make this patient very sick, plus it's gonna increase the costs because you're gonna then have to hospitalise your patient. So on the process of trying to save money, then you're gonna up much higher bills for hospitalisation. So I agree with Jo that there has to be a minimal finances to do it safely, and if that's not possible, best not to.

Yaiza Gomez Mejias: Back to the anaemia, you mentioned before, you started with this. When treating multiple myeloma with Melphalan, we often face haematological adverse attack.

Yaiza Gomez Mejias: So how do you differentiate between the haematological disturbances caused by the disease itself versus those caused by the drug?

Mariana Lopes: Typical clinical conundrum, isn't it? Usually we try to combine the bloods with other markers of remission, for example, for multiple myeloma cases they often can present with Hyperglobulinemia, and they will have a very high globulin levels at presentation.

Mariana Lopes: Let's say our patient was also anaemic at presentation and we started treatment and the hyperglobulinemia and the anaemia improved. We're getting disease control, and let's say at some point during treatment, we're becoming anaemic again. Then you're like, is this disease relapse? Is this now GI bleeding? What's going on here?

Mariana Lopes: Contextualising the other clinical information becomes very helpful because if your globulins are normal while your anaemia is developing, you could probably like, probably not disease relapse because the globulins have not increased as well. So potentially we're looking at chronic myelosuppression, or has this patient been on steroids for a very long time?

Mariana Lopes: That could again lean you towards more of a GI bleeding type situation. So that is a clinical challenge that we face pretty much every week. I think typically, we don't want to just do tests for the sake of doing tests. Sometimes we try to be as practical as we can. Let's imagine our patient's in remission and you feel like you can't afford to drop the steroids a little bit.

Mariana Lopes: You're not gonna risk relapse. You could just drop your steroids a little bit and add some gastric protectants. I know we don't want to add gastric protectants if you absolutely do not have to, but that's often a good test. If suddenly by dropping my steroids and adding, for example, some omeprazole, my anaemia is much better that was probably a little bit of GI bleeding. Or by reducing the chemotherapy intensity, does my anaemia get better as well? Maybe we're over-treating at this point so we can back off. However, if our patient is suddenly not doing so well, you know, maybe your globulins are coming up. Then in that case more likely to be relapsed.

Mariana Lopes: So you just have to take it all together. Sometimes it's hard. Sometimes you don't know. There's certainly been situations where we've gone back to repeating bone marrow samples and things like that. Sometimes it happens like we don't do that as a first line point of intervention 'cause that's more invasive and adds to cost, but eventually a big piece of your final answer.

Mariana Lopes: So yeah, that's your question and certainly a challenge.

Joanna Morris: It is the process of elimination. We have to rule out each of the options and finalise what we think the underlying cause is. Sometimes it's easier than other times.

Yaiza Gomez Mejias: I don't envy you, having that challenge very often must be very stressful. In your article you talk about toceranib which is very well known in the canine medicine, but we don't talk about it often in cats. What are the main indication of pros and cons general practitioners should wait when deciding whether or not to use it in cats?

Joanna Morris: So I guess it depends on the type of diseases that we're using it for. In cats, it's we're using in a more palliative way for carcinomas that we've failed with other treatments and we've got gross disease and things like that.

Joanna Morris: Occasionally for mast cells, they have to be multiple mast cells or worse type mast cells in cats. I, I think when we're using it in our practice, it is more for cats. The prognosis is slightly guarded. It's more end stage. Do you think Mariana? They do seem to tolerate it quite well. I don't think you should be shy of using it.

Joanna Morris: You're limited by the tablet size, small cats get a 10 milligrammes, bigger cats get a 15 milligrammes. Maybe you can alter the frequency of blood sampling to keep the costs down at once you've established the first month or so that they're tolerating it. You don't have to repeat the bloods quite so often, but it does, apart from the effects on appetite, it does seem to be quite well tolerated.

Mariana Lopes: I would agree. It's not like maximum tolerated dose chemotherapy. Unlike most chemotherapy protocols. It's ongoing. It's lifelong, so it's not the kind of protocol that you do for three months and then you stop. So we tend to reserve it for situations where we have something to monitor.

Mariana Lopes: Like we wouldn't want to put a patient on a lifelong treatment that doesn't currently have any active disease because the, the concern is what if you wouldn't need it? So we're always happier to use it if we have a patient that has, for example, an unresectable tumour or has metastatic disease or something that we can see the visible gross benefit.

Mariana Lopes: If it's shrinking or it's stable in size, or the patient had clinical signs and it doesn't anymore, despite still having that burden of disease, those would probably be the instances where we would use it the most in cats. I think most cats tolerate it very well and don't have some of those kind of annoying side effects.

Mariana Lopes: This is very, very important. Best tip is get a good nursing team 'cause

Joanna Morris: That's very important.

Mariana Lopes: We could not do any of this without our superstar nurses that are very good at giving pills to cats, would not be able to do it as much as we do without them.

Yaiza Gomez Mejias: It's a topic where we need a lot of communication with the caregivers and nurses play a really important role.

Mariana Lopes: Oh yeah. Could not do this job without our nurses.

Yaiza Gomez Mejias: No, definitely not. Thank you to you both, Mariana and Joanna, for sharing your expertise and reminding that the ultimate goal of these treatments is to prioritise a good quality of life for our feline patients. You can find the link to the full JFMS article in our show notes, and if you found in today's episode helpful, please subscribe and leave us a review and until next time, keep providing that excellent care to your feline patients. See you next month.