Chemotherapy for your cat

Although it can be frightening to learn that your pet has cancer there have been big advances in the treatment of cancer in animals. Chemotherapy is now a commonplace treatment for cancer in pets. If your cat is diagnosed with cancer it is possible that you will be offered some form of chemotherapy (perhaps alongside surgery or radiation therapy).

Chemotherapy is the use of drugs to damage and destroy cancer cells. Chemotherapy drugs can kill all cells (healthy ones as well as cancer cells) and great care is necessary when using them. There are many types of chemotherapy and depending on the drug they can be given by mouth, directly onto the lesion or given by injection into a body space or directly into the blood stream.

Different chemotherapy drugs are more effective against specific types of cancer and it is essential to get an accurate diagnosis of the type of cancer before the appropriate drug can be selected for treatment. Many vets in practice will refer patients to specialist veterinary oncologists when chemotherapy is being considered.

Chemotherapy is just a highly toxic drug given alone or in combination with other drugs. Your vet will try to find a treatment that is particularly toxic to a given type of cancer cell but less so to normal healthy body tissue.

Chemotherapy is given at a dose that will kill as many cancer cells as possible without doing too much damage to normal tissue. Doses are given at intervals (which may be days, weeks or months apart) and during the interval healthy tissue is able to recover and regenerate. Unfortunately in most cases the cancer cells also start to recover and over time the cancer cells often develop a resistance to the drug that is being used for treatment.

Often more than one type of chemotherapy is given at the same time – the aim of this is to attack the cancer cells from two or more sides whilst minimising the amount of damage to normal tissue by using lower doses of each drug.

Cancers can be treated using a variety of therapies (surgery, radiation or chemotherapy) and often a combination of treatments is given. If your vet has recommended chemotherapy it will be because it is the most effective treatment for your pet. You may need to travel to a specialist oncology centre for treatment and some forms of chemotherapy are expensive, therefore it is important that you discuss all your concerns with your vet before treatment starts.

It is very important that if you begin a course of treatment that you are able to see it through to the end. Treatments must be given regularly so before agreeing to start treatment make sure you are able to give regular medication or can take your pet to hospital for regular treatment sessions as necessary.

In some cases you may be given tablets to give your pet at home. Remember that these drugs are potentially toxic and must be handled according to the instructions given by your vet. Drugs should always be handled with gloves and must be given according to the schedule prescribed by your vet. Obviously it is particularly important that these drugs are kept out of the reach of children and pregnant women should not be exposed to them. Other drugs have to be given by your vet in the veterinary hospital and you will need to take your pet for regular treatment appointments.

Chemotherapy protocols are carefully designed to maximise the beneficial effect and minimise side effects of the drugs. The drugs are given regularly with an interval that allows healthy tissue to recover between doses. It is therefore important that doses are not given too close together or too much damage can be done to healthy tissues. If you accidently give too many tablets in one dose or give the doses too close together you must contact your vet or veterinary oncologist immediately.

Everyone has heard stories of how unwell some people are whilst receiving chemotherapy and no-one wants this for their pet. However, there is a difference between human and veterinary medicine. In human medicine doctors are aiming to prolong life for as long as possible – this means that treatment in people is often very aggressive (high doses of drugs are used to kill the maximum numbers of cancer cells). The high dose of drugs used makes the side effects much worse. In veterinary medicine vets are trying to prolong only high quality life. In general doses of treatment are calculated to minimise any ill effects experienced by your pet.

All chemotherapy drugs can cause side effects but these vary depending on the type of drug and the way it works. Hair loss, a well-recognised (and much feared) problem in people, is rare in animals receiving chemotherapy. However, clipped hair may take longer to regrow and the texture of the hair coat may change. Many cats receiving chemotherapy will be given steroids as well; these typically have side effects of increased drinking and urinating.

Commonly, chemotherapy can cause damage to the bone marrow which may make animals anaemic or suppress their immune response. For this reason pets receiving chemotherapy are usually closely monitored with regular blood tests to monitor levels of blood cells.

Digestive system upsets (nausea with or without vomiting and diarrhoea) are caused by damage to cells lining the intestine. Effects can range from extremely mild diarrhoea to severe vomiting and bloody diarrhoea. In most cases these complications are short lived and can be managed quite simply with the use of drugs to control sickness. However it is very important to report such complications to your vet so that they can provide you with additional treatment and it may be necessary to reduce the dose of the chemotherapy to prevent these complications occurring after the next dose.

If you are concerned in any way about your cat’s health you should contact your vet immediately.

Many of the chemotherapy drugs have cumulative toxic effects (that means that the effect of each dose builds up in the body). Many of the drugs are processed or removed from the body by the liver or kidneys. Your vet may need to check liver and kidney function with regular blood tests, particularly if your pet is receiving drugs which can cause damage to these organs. One commonly used chemotherapy drug can cause damage to the heart muscles and if your pet is receiving this you may be asked to take them for regular ultrasound scans of the heart.