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Cancer treatment - lymphoma chemotherapy

Lymphoma is a cancer of the lymph cells and can arise almost anywhere in the body. Although it is always frightening to learn that your pet has cancer - lymphoma is one of the most commonly treated forms of the disease. Modern treatment protocols can be highly effective in controlling lymphoma and affected pets can have several years of normal life with appropriate treatment. In many people's mind the term 'chemotherapy' conjures up frightening images of people suffering with cancer (and the effects of treatment) - however the effects of chemotherapy in pets are usually very different.

Your questions answered

What is chemotherapy?

Chemotherapy is just a highly toxic drug given alone or in combination with other 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. When treating lymphoma 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.

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. 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.

Do I have to give the treatment at home?

There are many chemotherapy treatment plans (also known as protocols) that have been used for the management of lymphoma in cats. The most commonly used include Cyclophosphamide, Vincristine (known as Oncovin) and Prednisolone - this is often called the COP protocol. Sometimes another drug, doxorubicin (also called Hydroxydaunorubicin or Adriamycin), is added and this is called a CHOP or COAP protocol.

Treatment for lymphoma is usually a combination of tablets given at home and hospital visits for your vet to administer some drugs intravenously (directly into the blood stream). Remember that all these drugs are toxic and must be handled carefully. 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. 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.

What side effects might my pet suffer?

All chemotherapy drugs can cause side effects but these vary depending on the type of drug and the way it works.

Prednisolone
Prednisolone is a steroid but in cancer therapy it is given at very high doses initially. It would be usual for pets receiving prednisolone to drink more than normal and hence wee more often! The drug given to otherwise healthy animals is a potent appetite stimulant. However cats receiving chemotherapy may have a poor appetite due to the cancer or the other chemotherapy drugs and so excessive appetite may not be a problem.

Some pets are more affected by high doses of steroids and may have muscle weakness and show excessive panting. Stomach ulceration is also a potential side effect of high doses of steroids and may cause blood in the vomit or in bowel movements.

Vincristine (Oncovin)
Side effects are rare following treatment with vincristine. The drug is given by your vet into the vein in the leg - if the drug leaks out of the vein it may cause damage and soreness around the site of injection. Weakness and neurological changes are reported by people receiving vincristine but these are rare in domestic pets.

Cyclophosphamide (Cytoxan/Endoxana)
Like many chemotherapy drugs cyclophosphamide can reduce production of white blood cells by the bone marrow, making your pet more prone to infection. This effect usually starts around 1 week after treatment has been given, and reaches its lowest point at 10-14 days. The bone marrow should naturally recover and will usually have returned to normal function before the next dose of doxorubicin is due. Your vet will usually check blood samples regularly from your pet to ensure that the bone marrow is working properly.

You should contact your vet straight away if:

  • Your pet has a high temperature above (102°F) - if your pet has a fever they will usually be quiet and unwilling to eat
  • Your pet is unwell (even without a high temperature)

Nausea and vomiting have been reported but in most cases this is mild and usually resolves without any treatment.

Hairloss following chemotherapy is not common in pets. Certainly clipped areas may take longer to regrow if your pet is receiving chemotherapy.

The main problem with cyclophosphamide is the risk of a form of cystitis. This is caused by irritation of the bladder by the chemicals formed when the drug is broken down in the body. To try to prevent cystitis the drug should be given in the morning and the dog should be encouraged to empty their bladder before bedtime. If you see any blood in the urine or your pet shows any signs of cystitis (frequent urination, discomfort on urination, or frequent squatting or straining) do not give any more cyclophosphamide until you have spoken to your vet.

Doxorubicin
Doxorubicin may also affect bone marrow function and you should be alert for signs of infection or anaemia. Doxorubicin can also reduce the production of other cells from the marrow, eg platelets (which help the blood to clot). Call your vet if your pet has any unexplained bruising or bleeding, such as nosebleeds, blood spots or bleeding gums.

Nausea can occur within a few hours of treatment with doxorubicin but this can be effectively controlled with drugs. If your pet is reluctant to eat or vomits after treatment make sure your vet knows. If your pet vomits after treatment do not offer them anything more to eat for 12 hours and then offer them a small tempting snack. Ensure that water is available and encourage them to drink if possible. Cats with diarrhoea should be allowed to eat as normal but if you are concerned or the diarrhoea continues for more than 24 hours call your vet for further advice. Some pets receiving doxorubicin are anorexic after treatment. This may be due to sores in the mouth or in some people the drug alters the taste of food and this may be unpleasant for some animals. Try feeding tempting small meals more frequently to encourage your pet to eat.

Hairloss can also occur after doxorubicin treatment but this is a rare complication and not of any clinical significance.

Lomustine (CCNU)
Lomustine can cause severe suppression of the bone marrow and regular monitoring of blood cell counts is important if your pet is receiving this.

Inappetence, vomiting and/or diarrhoea are also relatively common side effects but these can usually be controlled if the dose is tailored appropriately to the patient. 

Are there long term effects of chemotherapy?

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. Lomustine can cause liver damage and permanent bone marrow injury so long term monitoring by blood tests is required.

Doxorubicin 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.

Long term side effects of steroids are not uncommon but these are usually not a significant health risk. Skin may become thinner and darker in colour, hairloss is quite common and pets may develop a 'pot-bellied' appearance.

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