Lymphoma in Cats: Signs, Diagnosis, and Treatment

What lymphoma is

Lymphoma is a cancer of lymphocytes, white blood cells that are part of the immune system. Lymphocytes travel in the blood and lymph vessels and gather in the lymph nodes, the spleen, the lining of the gut, and other tissues. That is why lymphoma can affect one organ or several at once.

In cats, the digestive tract is the most common site. Intestinal lymphoma makes up about 50 to 70 percent of cases. Other forms affect the chest (called mediastinal lymphoma), the kidneys, the nose, the lymph nodes, the liver and spleen, the eyes, the skin, or the brain and spinal cord.

Vets also describe lymphoma by grade. Low-grade, or small cell, lymphoma grows slowly and is most common in the intestines of older cats. High-grade, or large cell, lymphoma grows fast and needs prompt treatment. The grade shapes both the treatment plan and the outlook.

Why some cats get it

Most cats with lymphoma are older, often 10 to 12 years old at diagnosis, but it can occur at any age. Lymphoma in the chest tends to affect younger cats, often around five years old.

Feline leukemia virus (FeLV) is the best-known risk factor. According to European feline guidelines, cats with FeLV are about 60 times more likely to develop lymphoma than cats without it, and about one in four cats with ongoing FeLV infection develops it. FeLV-related lymphoma tends to affect younger cats and often appears in the chest. Cats with feline immunodeficiency virus (FIV) are also more likely to develop cancer. FeLV-related lymphoma is seen less often than in the past, most likely because more cats are now tested and vaccinated. Today the intestinal form is the one vets see most.

Regular exposure to tobacco smoke is linked to a higher risk of intestinal lymphoma. Many cats with lymphoma test negative for both viruses, and in those cats no single cause is usually found.

Signs to watch for

Signs depend on where the cancer is. Intestinal lymphoma often starts slowly and can look like a long-running stomach upset. These are the changes owners most often notice.

• Weight loss, sometimes while the cat still eats
• Vomiting or diarrhea that keeps coming back
• Eating less, or walking away from food after a few bites
• Low energy, more sleeping, or more hiding
• Fast or labored breathing, with lymphoma in the chest
• Drinking and urinating more than usual, with lymphoma in the kidneys
• Nasal discharge, sneezing, or noisy breathing, with lymphoma in the nose
• Firm, enlarged lymph nodes, for example under the jaw
• Wobbliness, weakness, or seizures, with lymphoma in the nervous system

Many of these signs also fit more common problems, such as inflammatory bowel disease or kidney disease. A vet needs tests to tell them apart. Steady weight loss in an older cat is worth a checkup, even when the cat seems fine otherwise.

When it is an emergency

Lymphoma in the chest can make breathing hard, and this can get worse quickly. Take your cat to a vet or emergency clinic right away if it breathes with its mouth open, breathes fast while resting, or strains to breathe. The same applies to collapse, a seizure, or vomiting several times in one day.

A cat that has eaten little or nothing for a day should also be checked soon. Cats that go without food can develop a serious liver problem called fatty liver, and overweight cats are at higher risk. It is best to call your vet the same day and ask when to bring the cat in.

How vets diagnose it

The vet starts with a full exam, feeling the belly for thickened intestines or enlarged lymph nodes and listening to the chest. Blood tests and a urine test show how the organs are working and help rule out other diseases. The vet will usually test for FeLV and FIV at the same time. X-rays and ultrasound look for enlarged lymph nodes, thickened intestines, fluid, or masses.

To confirm lymphoma, the vet needs a sample of cells or tissue. A fine-needle aspirate collects cells with a thin needle and is a quick procedure. When that does not give a clear answer, a biopsy removes a small piece of tissue under anesthesia, either with an endoscope or during surgery. A biopsy also shows whether the lymphoma is small cell or large cell.

Tissue samples matter most for intestinal disease. Low-grade lymphoma and inflammatory bowel disease can look very similar, and a biopsy is usually needed to tell them apart. Further tests, called staging, show how far the cancer has spread. Your vet may refer you to a veterinary oncologist, a vet who specializes in cancer.

Treatment and outlook

Treatment depends on the type, grade, and location of the lymphoma and on the cat's general health. The goal is remission, which means the signs go away and the cancer can no longer be found on routine checks, with the cat eating and feeling well.

Low-grade intestinal lymphoma is usually treated at home with a steroid and a chemotherapy tablet. Most cats respond well. Reported remission rates range from about 70 percent to over 90 percent, and many cats live for two years or more.

High-grade lymphoma is usually treated with one of several injectable chemotherapy plans, given at the clinic over a period of weeks to months. Results vary a lot with the form of lymphoma. When a cat goes into remission, it often lasts several months to about a year. Cats with FeLV tend to do less well. Radiation therapy can work very well for lymphoma in the nose. For a single mass in the intestine, surgery is sometimes used together with chemotherapy.

If chemotherapy is not an option, a steroid on its own can ease the signs and improve quality of life for a while, often two to four months. It is a comfort measure and does not treat the cancer itself.

Cats usually handle chemotherapy better than people do. Hair loss is rare, and side effects such as vomiting or a poor appetite show up in only about one cat in ten. Chemotherapy can also lower the white blood cell count, so blood tests are part of the rechecks. Your vet can adjust the plan if side effects appear and will explain how to handle medicines and litter safely at home. Regular rechecks also help catch any return of the cancer early.

Other pets and people

Lymphoma itself is not contagious. A cat with lymphoma cannot pass the cancer to other cats, dogs, or people.

The viruses linked to it do spread between cats. FeLV passes through close contact, such as mutual grooming, bite wounds, and shared food bowls and litter boxes. A mother cat can also pass it to her kittens. FIV spreads mainly through bite wounds. There is no evidence that either virus infects people. If your cat with lymphoma tests positive for FeLV or FIV, ask your vet how to protect the other cats at home.

Lowering the risk

These steps lower the risk, though none of them prevents every case.

• Test every new cat for FeLV and FIV before it meets your other cats. A very recent infection may not show up at first, so your vet may suggest a second test some weeks later.
• Ask your vet about the FeLV vaccine. It is recommended for kittens and for adult cats at risk of exposure, such as cats that go outdoors.
• Keep your cat away from tobacco smoke.
• Keep your cat indoors, or supervise time outside, to reduce fights and bite wounds.
• Book regular checkups, and ask your vet how often an older cat should be seen. Weighing your cat at each visit helps catch slow weight loss early.

Testing matters for newly adopted cats. European feline guidelines report FeLV in under 1 percent of cats in northern and western Europe and in up to about 9 percent in parts of southern Europe. At Paw Squadron, every animal gets a checkup, treatment, vaccinations, and a microchip before adoption. Keep your cat's health records and bring them to your own vet at the first visit, so the vet can see which tests have been done. If you have questions about a cat you would like to adopt, send an adoption inquiry, or read more guides in PawPedia.