Published by: Ingrid King. Last Updated on: October 9, 2022 by Crystal Uys


Updated May 2022

Finding out that a beloved cat has cancer is heartbreaking for cat parents. The sad reality is that cancer is one of the leading causes of death in older cats. According to the Animal Cancer Foundation, 6 million cats will be diagnosed with cancer in the United States along. However, a cancer diagnosis does not have to be the end of the road. In fact, just like with humans, treatment is often possible, and chemotherapy may be one option that can allow your cat to live comfortably for many months and even years.

How does chemotherapy work?

Chemotherapy uses drugs with the objective to kill cancer cells with the least possible amount of damage to normal, healthy cells. In human medicine, the goal of chemotherapy is to achieve a cure. In pets, chemotherapy is aimed at controlling the disease and achieving a period of remission. Chemotherapy is typically used for cancers that affect multiple sites. Lymphoma is the most common form of feline cancer that is treated with chemotherapy. The drugs used in veterinary chemotherapy are frequently the same drugs used in human medicine.

How is chemotherapy administered to cats?

Chemotherapy drugs are administered in several different ways, depending on the type of cancer and the drug used. Options include

  • Oral – Given by mouth
  • Intravenous – Injected directly into the vein
  • Intralesional – Injected into the tumor
  • Intramuscular – Injected directly into the muscle
  • Subcutaneous – Injected under the skin to be slowly absorbed into the bloodstream

Chemotherapy usually doesn’t require hospitalization, but your cat may have to stay at the clinic for at least a couple of hours so vets can monitor any potential adverse reactions to the drug.

What about chemotherapy side effects?

Cat parents often recoil from the mere hought of putting their cat through chemotherapy. “Don’t be fearful of chemo,” said Conor J. McNeill, DVM, Dipl. ACVIM (Oncology), an oncolgist at the Hope Center for Advanced Veterinary Medicine in Vienna, VA. “Depending on how it is given, chemotherapy in cats generally can have few or no side effects.” Dr. McNeill frequently sees cat guardians who have been through cancer treatment themselves, and they don’t want to relive their own experience through their beloved cat.

Most cats tolerate chemotherapy extremely well. Some cats may experience side effects such as vomiting, diarrhea or poor appetite, but these side effects are usually mild and can be managed with supportive care. Only a very small number of cats on chemotherapy will require hospitalization due to the side effects of chemotherapy. Unlike humans, cats will not lose all their hair. Most cats will lose their whiskers, and shaved hair will be slow to grow back, but substantial hair loss is uncommon. Dr. McNeill is proactive about treating possible side effects such as pain and nausea. “This becomes especially important with cats,” says McNeill, “since they’re so good at hiding symptoms.”

How will you know whether chemotherapy was successful?

A cat in remission doesn’t look any different from a cancer-free cat. Typically, a successful remission means that lymphnodes will go down to normal size, and if there were any signs of illness that were related to the cancer, they will disappear. Remission can last anywhere from weeks to months, and for some lucky cats, even several years.

How to make the chemotherapy decision

Deciding whether chemotherapy is right for your cat is a very individual decision, and is best reached by talking to your vet and/or a veterinary oncologist. Factors that come into play are:

  • Prognosis: what is the prognosis for your cat’s particular cancer? How much time will you gain with your cat by treating the cancer?
  • Your cat’s lifestyle: is your cat extremely fearful of going to the veterinary clinic? Cancer treatment will involve frequent vet visits and blood tests, and you’ll have to weigh how this will affect your cat’s quality of life.
  • Finances: costs for chemotherapy can climb into the thousands of dollars. Making treatment decisions can be challenging for cat guardians when financial concerns have to be considered in addition to quality of life issues.
  • Palliative care: Sometimes, the right answer may be no treatment, and palliative care, which is aimed at keeping the cat comfortable with good quality of life for as long as possible, may be a better choice.

When it comes to deciding whether to choose chemotherapy for your cat, there is no right or wrong answer.

Eleven years ago, I wrote a post titled Chemotherapy for Cats. The post has received more than 900 comments to date and has turned into a forum for cat parents whose cats are going through chemotherapy to provide support to each other, ask questions, and share resources.

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