What is cancer?

Cancer is a term used to describe disease that is caused by a tumour – a collection of abnormal cells within the body thatcontinue 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.

Some tumours do not spread to other parts of the body and tend not to invade other surrounding tissues - these are termed ‘benign' tumours. In contrast to this, 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 (or ‘metastasise'), typically spreading via the blood stream or lymphatic system. Because of their more invasive nature, malignant tumours (cancers) are generally more serious than benign tumours, often causing more serious and extensive disease.

There are many different types of cancer, and they are often 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.

What causes cancer?

As is often the case in human medicine, 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. Inherited (genetic) susceptibility to the development of certain tumours almost certainly occurs in cats, although little is known about this at present. During a cats' 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 (carcinogens) – 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, and feline leukaemia virus is probably the best

example of this. Fortunately this is now quite a rare, but 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 (related to human immunodeficiency virus) also on occasions can lead to the development of cancer. Fortunately it is easy for your vet to test for the presence of both of these viruses.

When cancer is diagnosed, a natural and common reaction is ‘What have I done wrong?' or ‘What could I have done to have prevented this from happening?' While these are entirely natural responses when we first learn that

our pet has cancer, it is important to remember that in the vast majority of cases we don't know what will have lead to the development of the cancer, and therefore it would have been impossible to prevent.

What are the 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. In general, 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.

How is cancer diagnosed?

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 radiographs (Xrays) or ultrasound examination is 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 (surgical removal of a small piece of affected tissue) 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.

With some cancers, occasionally more sophisticated techniques may be required to either make (or confirm) the

diagnosis, or to plan the most appropriate treatment. Computed axial tomography (so-called ‘CAT' or ‘CT' scans)

or magnetic resonance imaging (MRI scans) are becoming more widely available for pets and can be very valuable, especially, for example, in the diagnosis of brain tumours, and in assessing the extent of tumour invasion.

Can cancer be treated?

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 (these are covered in more detail in Cats and Cancer 2). 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.

What are the common cancers that affect cats?

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

Lymphoma

Lymphoma (malignant lymphoma, lymphosarcoma) is probably the single most common cancer that affects cats.

This is a solid tumour of a type of white blood cell (lymphocyte) that is involved in immune responses. In addition to being present in the blood, there are accumulations of lymphocytes that occur elsewhere in the body – either in discrete sites (lymph nodes or lymph ‘glands') or within other tissues. Because of the wide distribution of lymphocytes in the body, lymphoma (malignant tumour of the cells) can occur at virtually any site, and also commonly occurs at multiple sites. Common sites to be affected include the lymph nodes (distributed throughout the body), the chest cavity, the intestinal tract, the nose, the kidneys and the nervous system. Clinical signs vary according to the tissues that are affected. Both infection with leukaemia virus and immunodeficiency virus can be underlying or predisposing causes of lymphoma development.

Various treatment options are available for lymphoma including surgery, drug therapy and radiation therapy. The

treatment choice will depend on the site and form of the tumour, and the availability of the treatment options. In

many cats the response to therapy can be very good and long lasting, although few cases are genuinely ‘cured'.

Squamous cell carcinoma

Squamous cell carcinoma is a cancer of the skin. Exposure to sunlight is one trigger-factor for this cancer and it is seen more commonly in white cats, and cats kept in hot sunny countries. The tumour commonly affects the nose or the ears and can initially look like a small scratch or wound that won't heal. Spread (metastasis) of these tumours is uncommon but local lymph nodes are sometimes affected.

Early treatment of these tumours can be very successful and most commonly involves surgical removal or radiation therapy. For some tumours affecting the superficial layers of the skin local radiation therapy (applied via a probe touched onto the skin) can be very effective. The response to drug therapy (chemotherapy) is generally not very good. For some affected cats, an alternative to conventional surgery may be ‘cryosurgery' where the affected tissue is frozen using liquid nitrogen applied via a special probe, although conventional surgery and/or radiation therapy are usually preferred options.

Mammary carcinoma

This is a cancer affecting the mammary glands that is most commonly seen in entire female cats (although it can also be seen in male cats and spayed female cats). The tumour commonly affects more than one of the mammary glands, which often develop multiple firm swellings or nodules, and the tumours commonly cause ulceration of the skin. This tumour commonly spreads to the local lymph nodes and can also spread to the lungs.

Early treatment of small tumours is likely to be much more successful than if multiple or larger tumours are present. Treatment is usually by surgical resection of the tumour and associated tissues, and there may also be a role for chemotherapy in some cases.

Mast cell tumour

Mast cells are a type of cell widely distributed in the body. Mast cell tumours commonly affect the skin, the spleen

and/or the intestines. In the intestines, these are often aggressive tumours that cause blockage of the intestine.

They can be removed surgically, but it is usually very difficult to remove the entire tumour and spread to lymph

nodes, liver, spleen, or the lungs is common. When mast cell tumour affecting the spleen is diagnosed, there is often also spread to other organs (liver, lymph nodes, bones marrow). However, surgical removal of the spleen alone can produce good disease-free survival times (often around 12 months) in many affected cats.

Mast cell tumours affecting the skin can be solitary masses or multiple nodules, and these may ulcerate. Surgical

removal is usually curative and some may spontaneously regress. Radiation therapy may also be used for some of these tumours.

Oral squamous cell carcinoma

This is a cancer arising from the cells lining the mouth or throat – it often involves the tongue, and the tumour

sometimes invades the local bone and can spread to local lymph nodes. The tumour usually causes progressive difficulty in eating, and there may also be intermittent or continual drooling and possibly halitosis (a bad smell from the mouth). These tumours can be difficult to treat but may potentially respond to surgery or radiation therapy where appropriate.

Fibrosarcoma/sort tissue sarcoma

These cancers form from the fibroblasts and other supporting tissues, most commonly arising beneath the skin.

They commonly present as gradually enlarging firm masses under the skin. The degree of malignancy of these tumours varies – some are highly malignant with extensive local invasion of tissues, and early metastases occurring to lymph nodes and the lungs. Others are less aggressive and will not be so invasive or metastasise so readily.

Optimum treatment usually involves a combination of surgery with radiation therapy and/or chemotherapy, although the prognosis is variable.

Osteosarcoma

Osteosarcoma is a cancer affecting bones. Bones in the limbs or the spine and skull can be affected, and where the limbs are involved the cancer often leads to weakening of the bone which may result in it becoming fractured (broken), with severe pain and lameness. Even without a fracture developing, most cases of osteosarcoma will produce progressive pain and lameness.

Osteosarcomas can spread (metastasise) to local lymph nodes and to the lungs, but this does not necessarily occur, and because of this, surgery (where possible) may be curative in these cases. Radiation and drug therapy may also be of value in some cases.

Respiratory (lung or nose) carcinoma

A number of cancers can affect the respiratory tract, but the most common are lymphoma in the nose, or

adenocarcinoma affecting the nose or the lungs. Tumours in the nose often cause progressive obstruction to the flow of air, and often result in snorting/snoring noises during breathing. There may be sneezing and discharge from the nose, and as the disease progresses there will be difficulty in breathing. Adenocarcinoma affecting the lung can cause difficulty in breathing, coughing, or a mixture of the two – the cancer can sometimes spread to the bones in the toes and cause lameness.

For lung tumours, surgical removal may be possible and this may be combined with chemotherapy, although by the time these tumours become apparent there has often been extensive spread within the chest. For nasal tumours, generally radiation therapy with or without chemotherapy is likely to be the best treatment.

Intestinal adenocarcinoma

Adenocarcinomas can affect either the small intestine or the large intestine. They are usually quite rapidly growing tumours that often cause disease due to partial blockage of the intestine (loss of appetite, weight loss, vomiting and diarrhoea are the most common signs). Metastasis to local lymph nodes is common, and the tumours often invade the intestine quite extensively.

Surgical removal is the treatment of choice. Additional chemotherapy is used in some cases although the efficacy of this is uncertain. Long survival times can be achieved in some cases (with surgery alone) even where the tumour has already spread to local lymph nodes.

Pancreatic and liver (bile duct) adenocarcinoma

Cancers affecting the liver and/or pancreas are fortunately not very common in cats. These tumours can cause jaundice (due to obstruction to the flow of bile), depression, weight loss, vomiting and distension of the abdomen (either due to the tumour or due to accumulation of fluid in the abdomen). The prognosis for these tumours is very poor with little response being seen to current treatments.