Chemotherapy For Cats

Cancer is the uncontrolled division of cells in or on the body. Any type of cell can potentially become cancerous. There are many reasons cancer occurs, including viral infections, exposure to carcinogens, which are cancer-causing substances (toxins, chemicals, cigarette smoke etc.), genetics, age, and diet, to name a few.

Cancer terms:

  • Tumour or neoplasm – A growth, it may be cancerous or non-cancerous.
  • Benign – A growth that doesn’t spread to other parts of the body.
  • Malignant – A growth caused by out of control cells that can spread to other parts of the body.
  • Oncology – Referring to cancer and its treatment.
  • Metastasis – Cancer which spreads to other parts of the body.

What is chemotherapy?

Chemotherapy is a drug to treat cancer, which targets rapidly dividing cells. Unfortunately, these drugs don’t discriminate between cancer and other types of cell which divide rapidly; this is why hair falls out in people undergoing chemotherapy.

Chemotherapy is a medical treatment that is used in conjunction with surgery and/or radiation therapy.

  • Before surgery to shrink the tumour.
  • After surgery to kill any cancerous cells left behind.
  • Some cancers (such as cancers of the blood or cancers which are not possible to remove with surgery), chemotherapy may be the only treatment.
  • To treat cancer that has spread (metastasised).

Several drug options are depending on the type of cancer the cat has. Chemotherapy may be administered as single-agent chemotherapy (one type of drug is used) or multi-agent chemotherapy where a combination of chemotherapy drugs are used.

Chemotherapy isn’t always going to cure your cat of cancer, but it can slow down the progression of the disease and buy your cat more time. For example, I had a cat with inoperable bone cancer, we always knew that cancer would kill her, but giving her chemotherapy meant that we were able to have a few more months with her.

Metronomic chemotherapy

A new and promising therapy in the treatment of cancer is metronomic chemotherapy. The oncologist administers traditional chemotherapy at the maximum tolerated dose (MTD). This is the highest dose possible to target the cancer cells while avoiding unacceptable side effects. As chemotherapy targets rapidly dividing cells, breaks in treatment are necessary to allow other rapidly diving cells such as bone marrow cells and cells which line the gastrointestinal tract to recover. Unfortunately, this also allows tumour cells to also recover, and develop drug resistance, which makes it a difficult balancing act.

Metronomic chemotherapy involves the continuous (daily or every other day) oral administration of traditional chemotherapy drugs at much lower doses and without the typical drug-free break. This interrupts tumour angiogenesis (formation of new blood vessels are necessary for sustained tumour growth and which enable tumour cells to break off and travel to other parts of the body). By targeting rapidly dividing endothelial cells which line the blood vessels, blood supply, which supports the tumour, is cut off which starves the tumour and prevents cells from spreading to other parts of the body (metastasis).

Metronomic chemotherapy isn’t a cure; the goal is to slow down the progression of incompletely resected (removed) or tumours that have spread.


An emerging therapeutic which shows great promise for the treatment of skin tumours. Chemotherapy drugs are poorly absorbed, but this treatment allows for better penetration by delivering electric impulsions into the tumour after administration of chemotherapy. More information can be found here.

Common chemotherapy drugs

Drug Brand name Treats Side effects
l-asparaginase Elspar Lymphoma (most commonly, high-grade) and some mast cell protocols GI disturbances, pancreatitis, liver toxicity, coagulation defects
Carboplatin Paraplatin Carcinomas and sarcomas Bone marrow suppression and GI disturbances
Chlorambucil Leukeran Lymphocytic leukemia, T cell lymphoma, multiple myeloma, lymphangiosarcoma, mast cell tumour and cutaneous plasmacytosis Bone marrow suppression and GI disturbances
Cyclophosphamide Cytoxan, Neosar Lymphomas, leukemias, carcinomas and sarcomas Bone marrow suppression and GI disturbances
Doxorubicin Adriamycin, Doxil Lymphomas, leukemias, carcinomas and sarcomas Bone marrow suppression, cardiac toxicity, GI disturbances
Methotrexate Otrexup, Rasuvo, Rheumatrex, Trexall MTX, Amethopterin Lymphoma and solid tumours (osteosarcoma) GI disturbances, bone marrow suppression
Lomustine Gleostine, CeeNu CNS neoplasms, mast cell tumours, histiocytic sarcomas and as a rescue agent for lymphoma protocol Bone marrow suppression, liver toxicity

References: Plumb, Donald C. (2018) Plumb’s Veterinary Handbook. 9th Edition.

Other uses for chemotherapy

Autoimmune diseases such as pemphigus may be treated with chemotherapy to suppress the immune system.

How is chemotherapy administered?

Chemotherapy comes in tablet or injection form. Your veterinarian may refer you to a specialist treatment centre as not all veterinarians can administer chemotherapy at their practice. Most chemotherapy is administered via intravenous injection (into a vein), into a body cavity (such as the chest) or oral chemotherapy drugs which can be administered at home or by a veterinary nurse if you are not confident giving pills.

Before your cat receiving chemotherapy, he will have routine bloodwork done to check his white blood cell count, red blood cell count, and platelet counts. Your veterinarian will delay chemotherapy if the blood counts are too low.

Most chemotherapy is given on an outpatient basis, for cats who are receiving IV chemotherapy, the cat will visit the practice, undergo bloodwork, and chemotherapy treatment and will be discharged within an hour.

Chemotherapy side effects

Chemotherapy doesn’t have as many side effects in cats as it does in humans and cats don’t lose their hair as we do.

As chemotherapy drugs target fast-growing cells, other cells such as those in the gastrointestinal tract and the bone marrow will also be targeted.

  • Gastrointestinal upset: This typically presents as nausea (loss of appetite, drooling, lip-smacking), vomiting and diarrhea. The veterinarian may recommend a combination of fasting for 12 hours along with anti-nausea medication (maropitant, known as Cerenia) and appetite stimulants.
  • Bone marrow suppression: Chemotherapy can cause a reduction in blood cell counts (red blood cells, white blood cells and platelets), white blood cells are affected most often. WBC numbers can drop a week after chemotherapy which can make the cat more vulnerable to infection, watch for signs such as vomiting, diarrhea, loss of appetite, fever, and lethargy. The veterinarian will monitor your cat’s blood cell count during chemotherapy treatment and if the WBC count drops too low, may prescribe antibiotics to help fight infections.
  • Lethargy: I always found my cat would be quite lethargic for 1-2 days after she had received chemotherapy.
  • Increased urination and thirst: Some chemotherapy protocols include Prednisone, a steroid that can cause an increase in urination and thirst. Ensure there is plenty of fresh drinking water available at all times. Watch for signs of dehydration which can include dry gums, poor coat condition, and sunken eyes.
  • Hair loss: Mild hair loss can occur in cats, which affects the whiskers more than other types of hair, but it isn’t as severe as experienced in people undergoing chemotherapy as cats don’t have continually growing hair as humans do.

Keep a close eye on your cat and if you notice any symptoms, seek veterinary advice immediately.

How often is chemotherapy administered?

This varies depending on the type of cancer and the treatment options, but it can range from weekly to every month or so.

Should I give my cat chemotherapy?

This is a tricky one, and it is up to you and your veterinarian to decide.

  • If the type of cancer is easy to treat, some cancers are more aggressive and/or do not respond well to chemotherapy
  • The overall health of the cat
  • The age of the cat

It is extremely important to find a veterinarian you can trust and who can guide you. They can’t make decisions for you, but they can give their opinion on what they feel is the best and kindest course of action to take. Advanced cancer may not be possible to treat.

Sadly, sometimes the cost also factors into your decision. Chemotherapy isn’t cheap, and not everybody can raise funds. Of course, the type of cancer and the stage all come into play. Some cancers are easier to treat than others, but certainly, the cost can come into play.


Your cat may not feel well for a day or so, so a bit of extra care won’t hurt. Be mindful that a cat can lose his or her appetite after chemotherapy. Try to encourage the cat to eat with special treats such as cooked chicken; this is particularly good because it is reasonably bland too. Warming up the food can also encourage him to eat.

The body excretes chemotherapy and its metabolites via the urine and feces, take care when cleaning litter trays. Always use rubber gloves when handling the litter tray or cleaning up accidents (vomit, feces, and urine). Pregnant or lactating women and children should avoid cleaning out litter trays anyway, but particularly in cats who are undergoing chemotherapy. Dispose of used litter in the garbage.

How safe is it to have a cat in the home who is undergoing chemotherapy?

Caregivers can continue to enjoy a close relationship with their cat during chemotherapy treatment and it is safe to stroke, hug and kiss your cat during this time. However, pregnant or lactating women should avoid contact for 3-5 days after chemotherapy treatment. Take care with litter trays, the metabolites of chemotherapy are excreted out of the body via the urine and feces, which typically lasts 3-4 days depending upon the chemotherapy drug used.

Your veterinarian may also have prescribed painkillers, anti-nausea medication and/or antibiotics while your cat is undergoing treatment. Always follow the instructions and administer as prescribed.

Frequently asked questions

Is it safe for cats to share a litter box?

Yes, it is safe for cats in multi-cat households to share litter trays with a cat undergoing chemotherapy. As per normal guidelines, there should be one tray per cat, plus one extra. Scoop out solids twice a day and empty once a week.

Use rubber gloves when cleaning litter trays and wash hands with soapy water afterwards.

Cleaning litter trays

Wear disposable gloves, remove solids and double-bag in impermeable disposable bags. Dispose of soiled litter along with the disposable gloves in the outside garbage bin.

What happens if my cat has an accident outside the litter tray?

Wear gloves to clean accidents, and wash hands well with soap and water afterwards. If the cat has an accident on his or her bedding, wash it separately from other laundry two times.

How to safely handle chemotherapy drugs

Some chemotherapy protocols require the caregiver to administer chemotherapy at home. This is usually a low-dose oral chemotherapy drug. Unlike other pills which pet-owners will sometimes break in half, or crush into the food, never do this with chemotherapy drugs as breaking it up can lead to inhalation of the residual chemotherapy drug.

Wear chemotherapy-rated gloves which the veterinarian should be able to supply.

Never store chemotherapy near human medications, food or where pets or children can access them.

Pregnant, lactating or planning to become pregnant

Avoid handling chemotherapy drugs and cleaning litter trays and avoid contact with your cat for 72 hours post-treatment. Speak to your physician if you have any additional questions.

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  • Julia Wilson, 'Cat World' Founder

    Julia Wilson is the founder of Cat-World, and has researched and written over 1,000 articles about cats. She is a cat expert with over 20 years of experience writing about a wide range of cat topics, with a special interest in cat health, welfare and preventative care. Julia lives in Sydney with her family, four cats and two dogs. Full author bio

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