Cancer in Cats – A Basic Overview

It is estimated that one in five cats will get cancer in their lifetime, which is slightly lower than the incidence of cancer in people and dogs. Feline cancer is commonly seen in veterinary practice; and is one of the leading causes of death in cats. This high prevalence may be partly because older cats are more prone to developing cancer and in modern times cats are living longer than in the past, largely due to improved health care and better diets.

There are many different types of cancer in cats and they vary widely according to where in the body they occur; how aggressive they are; their treatment options and prognosis. Today we take a brief look at what a diagnosis of this condition may mean for both a cat and the owner.

Cancer is the uncontrolled development of abnormal cells, with the potential to spread to other parts of the body. Cancers can be graded according to how abnormal the cells are and how quickly they grow. Malignancy refers to how readily a cancer will spread to other areas or invade surrounding tissues.

The first place that a cancer appears is referred to as the primary site, and metastasis refers to the development of secondary growths in other parts of the body. Secondary sites of cancer, or places where metastasis is likely to occur, tend to be where there is a high blood supply or level of lymphatic drainage, commonly the lungs and liver.

Most cancers do not have a clear cause, but may be associated with environmental factors, genetic predisposition, and biological factors such as age. The risk of certain types of cancer does increase substantially with specific predisposing factors. For example, mammary cancer is one of the most common cancers seen in both dogs and cats that are unsterilized, but it virtually disappears from populations where early neutering is the norm(2). Evidence suggests that environmental tobacco smoke increases the risk of certain cancers in cats and dogs(3); and chronic sun exposure is associated with the development of cancer on the face, ears and nose of cats that have little pigmentation in those areas(3).

Infection with Feline Leukaemia Virus (FELV) is strongly associated with the development of lymphoma in cats; and used to account for the majority of these cases. However, in the last couple of decades this link has weakened, as screening tests and vaccination against FELV became more commonplace in veterinary practice(1) and the prevalence of infection decreased (For more on this take a look at our blog on Feline Viruses: FIV and FELV).

There is no strong evidence at this stage which shows that certain breeds of cat are more predisposed to developing cancer than others. Unfortunately, the research available on cats lags behind that of dogs. Certain breeds appear to be over-represented in practice, but these are the most popular breeds and the increased incidence of cancers seems to correspond to their higher numbers within the general cat population rather than true predisposition.

From an evolutionary standpoint, showing symptoms of sickness made cats vulnerable to larger predators. For this reason, cats tend to hide illness, and the signs that something is wrong can be quite subtle.

Lumps and bumps are the most obvious sign of cancer present on or just below the skin, but these can also be benign, so not all lumps and bumps are necessarily dangerous. Internal cancers are more difficult to diagnose. Often the signs are quite vague and not specific to cancer. Weight loss in cats with cancer is common, as well as decreased appetite, vomiting or diarrhoea, lethargy, and a rough coat.

If your cat shows any of these symptoms it is worth a check up at the vet. There is no direct test for cancer in animals. Blood tests are helpful in checking organ function, and there are various types of diagnostic imaging that are useful tools in looking for cancer. If your vet finds a mass that may be cancerous they will most likely want to either perform a biopsy or a fine needle aspirate, which is when a needle is inserted into the mass and a few cells drawn out to examine microscopically. These tests can help to diagnose what type of cells are present, as well as malignancy and even the grade of cancer present. Biopsies are slightly more invasive, but are also much more accurate than fine needle aspirates.

If your cat is diagnosed with cancer the decision of how to proceed is both complex and personal. It depends largely on the type and grade of cancer; but is also influenced by you, the care giver, and of course your cat. Your financial situation and lifestyle are relevant, as are, importantly, factors about your cat. These include your cat’s overall health, as well as personality and the ability to cope with vet visits and cooperate with being medicated.

Investing in tests to get a definitive diagnosis of the type and grade of cancer is strongly advised as this clarifies what options there are going forward. Going to a veterinary oncologist for a second opinion can be extremely helpful as they are not only up to date with the latest treatment options; but can also help to choose an individual treatment plan that is best suited to your cat. From there, it is easier to navigate the best path for you and your cat, with thorough knowledge of what different treatment protocols would involve; what possible side effects may occur; costs; and prognosis.

Surgery is a common treatment option, depending on the site of the cancer. Chemotherapy is also used in cats, and to a lesser degree, radiation therapy. Cats tend to tolerate chemotherapy better than humans, and its aim is often for remission rather than cure, with quality of life being sustained. It is also possible to just give symptomatic or palliative treatment; and in some unfortunate cases, euthanasia is advised.

The many types of cancer vary significantly in their effect on the body; level of malignancy; treatment options; and prognosis. The more you know about the type of cancer, the better equipped you are to understand its effects and find the best treatment, regardless of whether the goal is curative or palliative. Having a veterinary opinion that you trust can make all the difference in finding the best way forward for you and your cat.

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References

1. Cat Health News. (2013, March 14). FELV and lymphoma in Germany. Winn Feline Foundation. Retrieved from: https://www.winnfelinefoundation.org/education/cat-health-news-blog

2. McKenzie, B. (2018, October 2). Is cancer increasing in cats and dogs? Veterinary Practice News. Retrieved from: https://www.veterinarypracticenews.com/evidence-based-medicines-october-2018

3. Vet Cancer Society. (2020). Are there environmental factors that contribute to cancer in dogs/cats? Veterinary Cancer Society. Retrieved from: https://vetcancersociety.org/pet-owners/faqs