Lymphoma in Cats: The Commonest Feline Cancer

Lymphoma is a cancer of the lymphocytes, a type of white blood cell that travels all through the body as part of the immune system. Because those cells turn up everywhere, the cancer can settle in different places, and in cats the pattern looks quite different from dogs.

The commonest site by a long way is the gut. Gastrointestinal lymphoma accounts for somewhere around 50 to 70% of feline cases (VCA Animal Hospitals, 2024), which explains why the early signs are so often weight loss, a fading appetite, vomiting or diarrhoea rather than anything you can see or feel. The other forms turn up less often. Mediastinal lymphoma sits in the chest and can cause breathlessness, renal lymphoma affects the kidneys, and nasal lymphoma shows up as a stuffy, snuffly nose or facial swelling. Most owners reading this will be facing the gut form in an older cat, so that's where I'll spend the most time.

If there's one thing to get clear about lymphoma in cats, it's this, and it's the bit that gets lost when people just hear "cancer". Gut lymphoma comes in two very different versions, and they behave almost like separate diseases.

Small cell lymphoma, also called low-grade lymphoma, is the indolent, slow one. It creeps in over months, sometimes overlapping so closely with inflammatory bowel disease that telling them apart needs a proper biopsy. It's manageable, often for a long time, and it sits behind those reassuring two-to-three-year figures.

Large cell lymphoma, also called high-grade or intermediate-to-large-cell, is the aggressive one. Signs come on fast, over days to weeks, your cat goes downhill quickly, and the outlook is more guarded (NC State Veterinary Hospital, 2024). It's a serious diagnosis, and I won't pretend otherwise.

Same word, two very different roads. Which one your cat has is decided by looking at the cancer cells down a microscope, and it's worth pinning that down before you weigh up anything else, because it changes the whole conversation.

Small cell vs large cell: why the type matters more than the word

Small cell (low-grade): slow, often months to develop, treated with two tablets at home (chlorambucil and a steroid), most cats respond and many live two to three years or more, usually feeling well. The hopeful form.

Large cell (high-grade): fast, days to weeks, treated with injectable chemotherapy (CHOP), around half to three-quarters respond but remissions are typically shorter, often a few months. The serious form, where comfort care is a very reasonable choice too.

If your cat has small cell lymphoma, the treatment is refreshingly low-key. It comes down to two oral medications: chlorambucil, a gentle chemotherapy tablet, and prednisolone, a steroid (NC State Veterinary Hospital, 2024). You give them at home, there's no drip and usually no hospital stay, and the biggest practical hurdle for most owners is simply getting tablets into a cat, which is a problem your vet can help you solve.

The numbers here are good. Around 70% of cats with low-grade intestinal lymphoma go into remission, and that remission typically lasts two to three years (VCA Animal Hospitals, 2024). In one study of 56 cats, around 86% responded to chlorambucil and a steroid, with a median overall survival of about three and a half years and side effects that were uncommon and generally mild (Pope et al., 2015). The medication is well tolerated, and most cats carry on eating, sleeping in their usual spots and being themselves throughout (NC State Veterinary Hospital, 2024).

This is the form with a lot to be hopeful about. It isn't a cure, since the cancer is being controlled rather than cleared, but "controlled, comfortable and at home for a couple of years or more" is a genuinely good outcome for an older cat.

The aggressive form needs a frank conversation. Large cell lymphoma is treated with a multi-drug injectable chemotherapy protocol, usually one called CHOP, given as a course over several months (NC State Veterinary Hospital, 2024). Between about 50 and 75% of cats with large cell gut lymphoma respond to CHOP, but the remissions are shorter, with survival commonly in the region of six to nine months (NC State Veterinary Hospital, 2024).

So this is a more guarded picture, and I'd be doing you a disservice to dress it up. Some cats do well and buy good extra time, and that's worth a great deal. Many, though, don't get the long stretches the small cell cats can. Choosing comfort-focused care instead of chemotherapy is an entirely reasonable, loving decision for this form, and our [guide to deciding whether to treat] takes that choice as seriously as the choice to go ahead. Neither is wrong.

One fear stops a lot of owners before they've really started: the picture of human chemotherapy, of a sick, bald, miserable patient. Please set that picture down, because it isn't what happens to cats.

Cats tolerate chemotherapy much better than people do. They very rarely lose their fur, they don't usually look or act ill, and only around 10% of patients have any side effects at all (VCA Animal Hospitals, 2024). When side effects do happen they're usually mild and temporary: a day or two of reduced appetite, a soft stool, a quieter mood (NC State Veterinary Hospital, 2024). Veterinary protocols are dosed for quality of life rather than pushed to the limit, and it shows in how well most cats sail through it. For more on this, [why pet chemo isn't human chemo] is worth reading before you let the human version make the decision for you.

Older information often tied lymphoma tightly to feline leukaemia virus (FeLV), and historically that was true. Before vaccination, FeLV was a major driver of the disease, the cats affected were often young, only a few years old, and the lymphoma tended to sit in the chest or the lymph nodes (Cornell Feline Health Center, 2024).

Widespread FeLV vaccination changed that picture dramatically. FeLV-associated lymphoma has become much less common, and the typical patient now is an older cat, most often around ten to twelve years old, with the gut form (Cornell Feline Health Center, 2024). The link hasn't vanished entirely, and certain forms still carry a strong FeLV association, with around 80% of cats with the chest (mediastinal) form testing positive (VCA Animal Hospitals, 2024). That's exactly why your vet will usually want to run a FeLV and FIV (feline immunodeficiency virus) test as part of the workup. It helps explain the picture, it matters for any other cats in your home, and it can shape the outlook.

The first and most useful step is finding out which type your cat has, because everything else flows from that. A small cell diagnosis opens a hopeful, home-managed road. A large cell diagnosis calls for a more careful weighing-up of treatment against comfort care, with no wrong answer in it.

Whichever form it turns out to be, the question worth keeping at the centre isn't how long, it's whether your cat is still enjoying her life, still eating, still seeking out the warm spots and the company she loves. That's something you can track rather than agonise over, and our [guide to measuring quality of life] shows you how to watch the trend instead of guessing day to day. For the gut forms especially, keeping weight and appetite up matters, and our [guide to feeding a pet with cancer] is built for exactly that. Start with the type, lean on the people treating your cat, and take the next decision when you get to it, not all of them tonight.