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Cancer in Cats

17th August 2018

Cancer in Cats

What is it and how is it diagnosed?

Cancer is a term used to describe disease that is caused by a tumour (or neoplasm) – 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.

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 generally 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 aggressive and invasive nature, malignant tumours (cancers) are generally more serious than benign tumours, often causing more serious and extensive disease, and are generally more difficult to treat.

Overall, cats suffer with neoplasia (or development of tumour[s]) less frequently than dogs. Neoplasms may perhaps be seen less than half as frequently in cats compared with dogs. However, when cats do develop tumours they are much more likely to be malignant (3-4 times more likely than in dogs) and therefore much more likely to cause serious disease.

The most common sites of cancer in cats include the skin, the white blood cells (leukaemia and lymphoma), the mouth, the stomach and intestines and the mammary glands.

Types of cancer

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 ‘leukaemia’ 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.

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:

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 relatively 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 (carcinogens) – but still in most individuals, the underlying causes and triggers for the cancer remains unknown.

We do know that some viral infections in cats can cause cancer, and feline leukaemia virus (FeLV) is probably the best example of this. Fortunately, infection with this virus is now relatively uncommon in most places. However, when cats are exposed to this virus it 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), related to human immunodeficiency virus or (HIV) 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.

Studies suggest that compared with an uninfected cat, a cat that is infected with FeLV has an approximately 50-fold increase risk of developing lymphoma, and a cat infected with FIV has an approximately 5-fold increased risk.

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 led 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, vomiting, diarrhoea, 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 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?

You or your vet may suspect cancer to be an underlying cause of the clinical signs your cat is showing. However, the clinical signs and examination by your vet alone are not sufficient to be able to diagnose the condition.

Additional investigations in the form of radiographs (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 (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.

Treatment of cancer in cats

It is always extremely difficult when you learn that your cat has developed cancer.

There are often feelings of bewilderment and even guilt (‘how could I have prevented this?’), and it inevitably takes time to come to terms with the disease. Although for most tumours the underlying cause is simply unknown, for many (although not all), treatment may be available that will significantly improve both the quality and length of life for the cat.

While a diagnosis of cancer is never good news, it is not necessarily a ‘death sentence’ for a cat. Just as in human medicine, many treatment options are available, although not all cancers respond well to therapy and some may be extremely difficult to manage. The cat’s quality of life and potential suffering must always be the overriding concern – it is worthwhile discussing the options available in depth with your vet before arriving at any decision.

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 improvement in quality of life for affected cats. Treatments can carry side effects though, and your vet will be aware of these. The aim is always to improve the quality of life, and not to cause any increased suffering through the treatment. Although good results can be achieved for some cancers, it is not always appropriate or right to treat a cat and you should discuss options carefully with your vet.

Staging the patient

Before any treatment is begun for cancer, your vet will want to ‘stage’ your cat. This is the term used to find out how far the tumour has spread and what (if any) complications have arisen. Staging a tumour often involves taking X-rays (or doing an ultrasound) to see if there is evidence of spread (for example to the lungs or liver), perhaps getting samples (biopsies or aspirates) from local lymph nodes, and checking blood samples.

Quality of life for the cat with cancer

When treating cancer, it is important that everyone involved has the same goals in mind. Veterinary surgeons aim to provide an improved and good quality of life for the cancer patient without producing any unacceptable side-effects with treatment. Often this will also mean a longer life but unnecessary suffering and pain must be avoided. It helps to have talked in advance with your vet about what guidelines you can use to judge the quality of life by. For many cancers, inevitably there may come a day when you have to consider euthanasia to avoid unnecessary suffering – this can be a difficult and distressing time and having the support and help of your vet, and also friends and family, can be invaluable.

Treatment options for cancer in cats

Some treatments are widely available in general practice, while others are only available at specialist centres. Depending on what tumour has been diagnosed, your vet may sometimes suggest referring your cat to a specialist with expert knowledge and a greater range of treatment options. There are three main forms of therapy for cancer:

  • Surgery
  • Chemotherapy (drugs)
  • Radiation therapy

Which treatment is used (or offered) for any individual cat will depend on factors such as:

  • The type of cancer
  • The site of the cancer (where it is in the body)
  • The presence of metastases (distant spread of the tumour)
  • What is appropriate for your cat
  • What is available/accessible to you

If you have any doubts or questions, ask your vet for more information.

Surgery for cancer patients

Surgery is the single most common form of therapy for cancer and is the treatment most likely to result in a cure. However, complete removal of the tumour by surgery is not always possible (due to the site of the tumour or its spread to other sites). This is one of the reasons why an early diagnosis and early treatment can significantly improve the long-term prognosis.

In addition to ‘curative surgery’ (where complete removal of the tumour is attempted), surgery can also be used sometimes to remove some (but not all) of the tumour to help improve quality of life or to help with other treatments (such as chemotherapy or radiotherapy). You can discuss with your vet the risks and benefits anticipated with any surgery to help make a decision in the best interest of your cat. You can also discuss with your vet any pain relief (analgesic therapy) that can be given for the surgery and afterwards, and what sort of postoperative care would be required.

When cancer patients are treated surgically, it is common to remove normal tissue around the tumour as well as the tumour itself (this is referred to as ‘surgical margins’). The reason for this is that many tumours spread microscopically so although it may not be possible to see or feel any abnormalities, even normal tissues around a tumour may contain abnormal cells that would cause future problems if not removed.

Radiation therapy (radiotherapy)

Radiation therapy is a frightening concept for many people as it is often assumed there will be numerous side-effects. However, as with any form of cancer therapy for cats, the goal is to improve quality of life and to relieve any discomfort, without causing any unnecessary additional suffering. While radiation therapy is able to achieve this for many cat cancers, unfortunately the availability of this form of therapy is quite limited. Your vet may be able to refer you to a specialist centre for this treatment.

Radiation therapy most commonly involves what is known as ‘external beam radiation’ (similar to X-rays). A machine is used to focus a beam of radiation at the tumour, but the radiation is much more intense than X-rays and the radiation produced has the ability to kill off cancer cells. Because normal cells can be damaged too, careful calculation of the dose, frequency and targeting of the radiation is needed. At its best, radiation can kill off cancer cells while causing very little damage to surrounding tissues. Although radiation therapy is used to kill cancer cells, this does not mean that the treated cat becomes ‘radioactive’ and there is no risk whatsoever to people in contact with the cat.

External beam radiation therapy is typically delivered by a machine known as a linear accelerator

External beam radiation therapy is typically delivered by a machine known as a linear accelerator (pictured right). This therapy usually requires a short general anaesthetic (so that the cat does not move during the procedure), and generally several treatments are given (each lasting only a few minutes) over a few weeks.

Radiation therapy can cure some tumours, while with others it may reduce and help control the tumour. In most cases the damage to surrounding normal tissues is minimal and does not cause significant side effects. The specialist undertaking this therapy would discuss with you in detail what was involved before you make any decision. The radiation therapy itself does not hurt, and indeed it can be an effective way of providing pain relief if the cancer is causing pain. Skin irritation and hair loss at the site of radiation therapy is one of the most common side effects.

Another form of radiation therapy called brachytherapy is occasionally used, where sources of radiation are placed within or on the surface of the body (using a probe) to expose a tumour to radiation therapy. This can provide a more localised form of radiation therapy and can be used, for example, to treat some skin tumours such as squamous cell carcinoma.

Radiation therapy is often used in combination with surgery and/or drugs (chemotherapy), and some drugs have the ability to enhance the effectiveness of the radiation therapy.

Chemotherapy (anti-cancer drug therapy)

As with radiation therapy, the thought of chemotherapy often carries many misconceptions. Many people know of friends or relatives who have received chemotherapy for cancer and have experienced significant adverse effects associated with the treatment. Although anti-cancer drugs can, and do on occasions, produce side effects in animals too, most people are surprised and relieved at how well cats tolerate chemotherapy. This is in part because cats do tolerate the treatment better, but also in part because lower doses are often used to avoid side effects that would affect the quality of life.

A wide variety of different drugs are available to treat cancers, the choice depending on:

  • the tumours being treated
  • what is available
  • how well the cat may tolerate the treatment

Your vet will be able to discuss these options with you and refer you to a specialist for further advice or treatment if necessary.

For many cancers a combination of different drugs are used to increase effectiveness (attacking the tumour in different ways), and to reduce the risk of side effects (using different drugs usually allows lower doses to be used).

Most chemotherapy drugs work by interfering with the ability of cells to divide (cancer cells have uncontrolled, continual growth and division). Side effects, when they occur, may be due to interference with other cells in the body that also divide rapidly, such as cells in the bone marrow, the intestinal tract and the skin. Side effects include:

  • Suppression of the bone marrow – this causes a low white blood cell count. The type of white blood cell usually affected first are known as neutrophils. Regular blood samples are usually taken to monitor the white blood cell count (usually 7–10 days after the drug is given). If the neutrophil count falls too low, the dose and/or frequency of the drug is usually reduced, and antibiotics may be temporarily prescribed. Platelets (cells in the blood associated with clotting) may also sometimes be affected by chemotherapy, and these too are checked when routine blood samples are taken.
  • Hair loss – although this can be one of the most obvious side effects of chemotherapy in humans, hair loss in cats is unusual. Where it does occur, often just the whiskers on the face are affected. Generalised hair loss is extremely rare.
  • Gastrointestinal irritation – a number of chemotherapy drugs can cause irritation to the stomach and intestinal tract for a few days after being given. This may result in nausea and vomiting, or sometimes just as lethargy and inappetence. Where this occurs the dose of the drugs can be altered and/or other medications can be used to overcome these effects. It is helpful to keep a diary of your cat’s behaviour while it is receiving chemotherapy, including a note of any vomiting or diarrhoea, and the cat’s appetite. If ever you are concerned about possible side effects associated with treatment, contact your vet immediately.

Other side effects generally depend on the drug being used – some have the potential to damage the kidneys, or the heart and thus monitoring or careful use may be required. However, in general less than 20% (one in five) treated cats will experience any side effects.

Some drugs are given as tablets, but others are given as injections by your vet – these injectable drugs are often given through a catheter that will temporarily be placed into a vein (usually in a leg).

Precautions in cats receiving chemotherapy

Because anti-cancer drugs can affect healthy as well as cancerous cells (in humans as well as cats), unnecessary exposure to these drugs should be avoided wherever possible. This includes unnecessary handling of the drugs, but also exposure to the drugs in urine and faeces that are produced by a cat being treated (and also other body fluids like saliva and vomit). If some simple precautions are taken, this exposure and any consequent risks can be reduced to an absolute minimum:

  • Giving tablets at home – your vet will warn you if he or she is prescribing tablets for you to give at home that are potentially harmful. If this is the case, these tablets (or capsules) must not be split or crushed – they will have a protective coating designed to prevent you coming into direct contact with the drug itself. Ideally the tablets should be handled and administered while wearing disposable gloves. If your cat spits out a tablet, this can be picked up (wearing gloves), wrapped in kitchen paper and then flushed down the toilet.
  • Dealing with urine and faeces – most drugs are eliminated from the body in the urine and/or faeces, and in general the concentrations of the drug will be highest in the first few days after treatment. Even early on, the amount of drug excreted is actually very low, but it is safest to wear disposable gloves when cleaning a litter tray and to place soiled litter in a sealed bag in the dustbin. If your cat urinates and defecates outdoors, no special precautions will be necessary
  • Dealing with soiled bedding – soiled bedding (with urine or faeces) should be washed separately from any other routine washing, and similarly food and water bowls should be washed separately from your own bowls and utensils

These simple precautions will help to make sure that any potential exposure to these drugs is kept to an absolute minimum.

General and palliative care for the cat with cancer

As already noted, it is useful to keep a diary of your cat’s behaviour, appetite, and any abnormalities you observe, as well as a note of when (day and time) you administer any medications. This will help you and your vet determine if any additional treatments or investigations are necessary.

Maintaining good nutritional intake is an important part of the supportive care for your cat with cancer, and offering a variety of foods can help to ensure that a good appetite is maintained. In general, good quality commercial foods are the best choice for a cat with cancer, although at times there may be some special dietary requirements to take into consideration. Warming the food may encourage the appetite, but occasionally, depending on the circumstances, temporary use of an appetite stimulant or a feeding tube may be needed to overcome poor food intake. Always talk to your vet if your cat’s appetite is reduced as this can indicate an underlying problem such as uncontrolled pain or side effects associated with the treatment being received.

Ensuring a good quality of life that is free from pain is the main goal in managing cats with cancer. Supportive therapy can be an important part of this, and such treatments may include use of:

  • Analgesic drugs – these are painkillers and can be important if there is any pain or discomfort associated with the cancer
  • Non-steroidal anti-inflammatory drugs (NSAIDs) – these drugs are anti-inflammatory and also help to relieve pain. They can be helpful in the management of some tumours for both of these reasons, and in addition NSAIDs may have a direct anti-cancer effect in some types of tumours (although this effect is not usually profound)
  • Anti-emetic drugs – these are drugs that reduce nausea and vomiting and may be needed in some patients
  • Antibiotics – if secondary bacterial infections become a problem or if your cat develops a very low white cell count (leaving them vulnerable to infection) antibiotics may sometimes be used

Never be afraid to ask questions and to find out as much information you can about your cat’s cancer and treatment options, and if there is ever anything you are concerned about regarding the cancer or potential treatment side effects always contact your vet immediately.

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