Chemotherapy For Cats: General Treatment Information

What is chemotherapy?   How is chemotherapy administered?   Side effects   Is chemotherapy expensive?   How often is treatment given?   Aftercare


Chemotherapy for cats

Before we begin, a very brief lesson in cancer. 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.

Common terms used in cancer:

  • Tumour – A growth, it may be cancerous or non-cancerous.
  • Benign – A growth which doesn’t spread to other parts of the body.
  • Malignant – A growth caused by out of control cells which 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 which is used in conjunction with surgery and/or radiation therapy.

  • Prior to 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 can’t be surgically removed), chemotherapy may be the only treatment.
  • To treat cancer that has spread (metastasized).

There are a number of drug options depending onthe type of cancer your cat has. In some cases, a combination of drugs will be necessary.  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 the 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 tumor 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 spreading to other parts of the body (metastasis). Along with sparing bone marrow and gastrointestinal tract cells, normal blood vessels are spared as they are less active than tumour blood vessels.

Metronomic chemotherapy isn’t a cure, the goal is to slow down progression of incompletely resected (removed) or tumours which 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.

Other uses for chemotherapy:

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

How is chemotherapy given?

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. Oral chemotherapy drugs are given by the pet owner at home.

Prior to 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.

Side effects:

Chemotherapy doesn’t have as many side effects in cats as it does in humans. They 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.

Some side effects can occur, these may include:

  • Nausea: This typically manifests as loss of appetite, drooling, lip licking and swallowing. The veterinarian may recommend a combination of fasting for 12 hours along with anti-nausea medication (maropitant, known as Cerenia). After 12 hours, introduce small but frequent meals.
  • Vomiting and diarrhea: A similar protocol to above, your veterinarian may recommend you withold food for 12 hours and then introduce a bland diet along with anti-nausea medication.
  • Decreased white blood cell count: This can make the cat more vulnerable to infection, watch for signs such as vomiting, diarrhea, loss of appetite, fever, and lethargy. Seek veterinary care if any of the above develop, they may prescribe antibiotics.
  • 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 which 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: Some hair loss can occur in cats but it isn’t as severe as experienced in people undergoing chemotherapy.

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

How often is treatment?

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 one which 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 the 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 he may not feel like eating and try to encourage him to do so with special treats such as cooked chicken, this is particularly good because it is reasonably bland too. Warming up his food may also encourage him to eat.

The body excretes chemotherapy drugs via the urine, take care when cleaning litter trays.  Always use rubber gloves when handling the litter tray. 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.

Avoid contact with the cat for 2-5 days after treatment if you are pregnant or lactating.

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.


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