This cat has had successful treatment of skin cancer of the nose with locally applied radiotherapy

 

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 that is present. For the vast majority of tumours, the underlying cause is simply unknown, and therefore prevention is impossible. However, for many (although not all) tumours, once a diagnosis has been made treatment may be available that will significantly improve both the quality and length of life for the cat.

It is always worth discussing with your veterinary surgeon what the treatment options are for your cat and the particular cancer that has been diagnosed. Some treatments are widely available in general practice, while others are only available at specialist centres. Depending on what tumour has been diagnosed, your veterinary surgeon may therefore suggest that your cat would benefit from being referred to a specialist with expert knowledge and a greater range of treatment options. By being referred to a specialist, this may give you further opportunity to discuss and find out about the cancer and treatment options available, but in all situations, further tests or treatment will only be undertaken if you decide to have this done.

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. Ideally this will also mean a longer life, and this is usually achieved. However, a longer life that ultimately involves unnecessary suffering and pain has to be avoided. Inevitably a decision will be needed on whether euthanasia is the best or most appropriate option. This is a distressing time, and it helps to have talked in advance with your vet about this, and to know what guidelines you can judge the quality of life by. In addition to your vet, having the support of friends or family can be invaluable.

There are three main forms of therapy for cancer – surgery, chemotherapy (drugs) and radiation therapy. What is used (or offered) for any individual cancer will depend on many factors, including the type of cancer, its site in the body, the presence or absence of metastases (distant spread of the tumour), and what is available/accessible to you. If you have any doubts or questions, ask your veterinary surgeon for more information.

Surgery for cancer patients

Surgery is the single most common form of therapy for cancer and is the most likely treatment to result in a cure. It can have several different goals, depending on the circumstances but a cure (complete removal of the tumour) is not always possible as some tumours spread readily through tissues, or can spread to distant sites (metastasise). This is one of the reasons why an early diagnosis and early treatment can significantly improve the long-term prognosis. Surgery can therefore have a number of different goals:

Surgery itself can inflict some pain and suffering, and inevitably there are some risks involved with surgery (that vary between patients). Again, you can discuss with your vet the risks and benefits anticipated with 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 post-operative care would be required.

Radiation therapy

Radiation therapy is a frightening concept for many people as it is often assumed there will be numerous side-effects associated with

its use. 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. Radiation therapy is able to achieve this for many cat cancers. Unfortunately, the availability of radiation therapy is quite restricted and so your veterinary surgeon is likely to have to refer you to a specialist 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 that produced by an X-ray machine. The radiation produced has the ability to kill off cancer cells, but can also damage normal cells too. Thus by carefully calculating the dose and the frequency of radiation therapy, along with focusing the beam of radiation on the cancer being treated, it is possible to kill off the cancer cells while causing 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 requires a short general anaesthetic, and generally several treatments are given (each lasting only a few minutes) over a three to five week period. Radiation therapy has the ability to cure some tumours, while others can be shrunk and controlled with this therapy for a good period of time. Although inevitably some damage will occur to surrounding normal tissue, in most cases this is minimal and will 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 – medication will be used to control this if necessary. Side effects such as nausea and vomiting are extremely rare. Cats appear to tolerate radiation therapy better than most animals or humans. They develop less significant 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.

Depending on the type of tumour being treated, radiation therapy is often used in combination with surgery and/or drugs (chemotherapy). Some forms of chemotherapy will actually enhance the effectiveness of the radiation therapy.

Chemotherapy (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 tolerate the treatment better and in part because lower doses are sometimes used to avoid side effects that affect the quality of life.

A wide variety of different drugs are available to treat cancers, and the choice of drug again depends on the tumours being treated, what is available, and how the cat may tolerate the treatment. Your vet will be able to discuss this with you and if necessary refer you to a specialist for further advice and/or treatment. For many cancers a combination of drugs are used so that the dose of any one drug can be minimised (reducing the risk of side effects) and so that the cancer cells can be attacked in different ways.

Most (but not all) chemotherapy drugs work by interfering with the ability of cells to divide (one of the characteristics of cancer cells is their uncontrolled, continual growth and division). Side effects, when they occur, often arise as a result of 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 that may be seen with chemotherapy therefore include:

•  Suppression of the bone marrow - this causes a low white blood cell count. The cells usually affected first by this are white blood cells known as neutrophils. Where chemotherapy is being given that can affect the bone marrow, it is important that regular blood samples are taken to monitor the white blood cell count (usually seven to 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 hair loss can be one of the most obvious side effects of chemotherapy in humans, hair loss in cats is rare. Where it does occur, it is usually just the whiskers that are affected and generalised hair loss is extremely rare.

•  Gastrointestinal irritation – a number of drugs used to treat cats can cause irritation to the intestinal tract for a few days after their administration. This can be manifested as 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 present, 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 per cent (one in five) treated cats will experience any side effects.

Some drugs can be given as tablets, but others have to be given as injections by your vet. Some of these injections need to be given carefully into a vein (blood vessel) as they can cause severe irritation to tissues if injected outside a vein. It is therefore quite common for a catheter to be placed into a vein (usually in a leg) and for the drug to be injected through this – for some drugs the injection is a small volume, but for others it is dissolved in a large volume of fluid that is infused slowly. Most injectable forms of chemotherapy are administered at intervals of one to four weeks.

Do I need to take precautions if my cat is 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:

•  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, it is important that these tablets (or capsules) are not split or crushed – they will have a protective coat on them that is designed to avoid any 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.

•  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 here, 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.

•  Soiled bedding should be washed separately from any other 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

As already noted, it is useful to keep a diary of your cat's behaviour, appetite, and any abnormalities you observe (vomiting, retching, diarrhoea, lethargy, etc) as well as a note of when 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 also encourage the appetite, but occasionally, depending on the circumstances, a temporary use of a feeding tube may be needed to overcome the problems of poor food intake. Significant inappetence or complete loss of appetite can indicate an underlying problem such as uncontrolled pain, or side effects associated with the treatment being received, that requires further investigation. Your vet will be able to work with you to try to overcome such problems and provide the optimum care for your cat.

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 in addition to the use of analgesic ('pain-killing') drugs when necessary, other treatments may also be used (depending on the circumstances) including, for example, antibiotics where secondary bacterial infection may be a complication and anti-inflammatory drugs where swelling and inflammation associated with a tumour is problematic.

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.

 

Updated November 2008