Cancer Overview

Cancer is a term used to describe disease that is caused by a tumour, this is a collection of abnormal cells within the body that continue to grow and divide without control. This usually results in the development of masses (growths or lumps), which are mainly composed of the abnormal dividing cells.

'Benign' tumours do not spread to other parts of the body and tend not to invade other surrounding tissues. The term cancer is used to describe 'malignant' tumours, which often do invade surrounding normal healthy tissue, and may spread to other sites in the body - 'metastasise', usually spreading via the blood stream or lymphatic system. Malignant tumours (cancers) are more invasive and generally more serious than benign tumours, which often cause more serious and extensive disease.

There are many different types of cancer, and they are usually classified according to the origin of the type of abnormal cell they contain. Thus cancers known as 'carcinomas' and 'sarcomas' are solid tumours that arise from various different tissues, whereas ‘leukaemias' are cancers that affect the bone marrow where blood cells are produced and often cause large numbers of abnormal cells to appear in the blood stream.

‘Lymphoma' is a solid cancer caused by the growth of abnormal lymphocytes – a type of white blood cell that can also be found in tissues and is part of the immune system.

Causes of Cancer

The cause of cancer in any individual cat is often unknown, and indeed many cancers are likely to arise for a number of different reasons. Genetic susceptibility to the development of certain tumours almost certainly occurs in cats, although little is known about this at present. During a cat's life they may potentially be exposed to a number of different things that can trigger abnormalities within cells that may ultimately lead to development of cancer – this may include exposure to sunlight or to a wide variety of different chemicals – but still in most individuals, the underlying causes and trigger for the cancer remains unknown.

We do know that some viral infections in cats can cause cancer such as feline leukaemia virus. This virus can infect the blood-producing cells of the bone marrow, and can lead to the development of leukaemia or lymphoma. Infection with Feline Immunodeficiency Virus (FIV) also on occasions can lead to the development of cancer. Your vet can do a simple test for both of these viruses.

Clinical Signs of Cancer

Because cancers can affect any tissues in the body, the clinical signs that cats develop are extremely diverse and there are no signs that automatically suggest cancer is the cause of disease. Generally, cancers affect older cats more commonly than younger cats.

In many cases, cancers will grow over quite a long period of time, and initially there may just be vague signs of disease such as poor appetite, lack of energy and weight loss. In other cases there may be more obvious signs such as persistent lumps in or under the skin, changes in the eyes, unexplained bleeding or wounds that do not heal. As the disease progresses additional complications will usually develop that often relate to the tissues or organs mainly affected. Although cancer may often be one of the potential causes of a variety of different signs (especially in older cats), it is important to remember that many other diseases commonly cause the same signs

as cancer and that, even where cancer is diagnosed, there may well be treatment options that will enable control or management of the disease, at least for a period of time. However, as it is important to diagnose cancer early, it is vital to seek veterinary advice as soon as any abnormalities are noticed.

Cancer Diagnoses

Although you or your vet may suspect cancer to be an underlying cause of the clinical signs your cat is showing,the clinical signs and examination by your vet are not sufficient, alone, to be able to diagnose the condition.Additional investigations in the form of X-rays or ultrasound examination are often needed to identify the location and/or the extent of any tumour, but the diagnosis of cancer can only be made by the microscopic examination of tissues by an experienced pathologist. This will usually necessitate a biopsy by your vet, although in some cases it may be possible to make a diagnosis from either a 'fine needle aspirate' (a small needle is inserted into a mass to remove or ‘suck out' a few cells that can be smeared on a slide for examination) or a ‘needle biopsy' (where a larger needle is inserted into a lump to remove a very small 'core' of tissue). Occasionally other techniques are also used to obtain samples of the suspected abnormal cells so that a diagnosis can be made. Blood samples are a routine part of the investigation of any suspected cancer patient – partly to detect any adverse effects of the cancer, and partly to detect the presence of any other disease.


Although a diagnosis of cancer is never good news, it is not necessarily a ‘death sentence' for a cat. Many treatment options are available for cancers. Not all cancers respond well to therapy and the choice of whether or not to treat, and what to treat with, will depend on many factors. Some forms of therapy are only available at specialist centres, and your vet may suggest that he or she refers you to one of these places. In many cases, appropriate treatment of cancer can result in a significant prolongation of very good quality of life for cats. Treatments can carry side effects, but your vet will be aware of these, and the aim is always to improve the quality of life of affected cats, and not to cause any increased suffering through the treatment. Generally, with careful monitoring and assessment, significant side effects can be avoided.

It is not always right to treat a cat with cancer, and the cat's quality of life must always be the overriding concern – it is worthwhile discussing the options available in depth with your vet before arriving at any decision.

Common Cancers That Affect Cats

Because of the enormous variety of cancers that can affect cats, it is impossible to list all the different types and their common manifestations. However, some of the most commonly encountered cancers include the following:


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