Chemotherapy and radiation for pets Print E-mail
News - Rubrieke
Monday, 24 June 2013 13:57
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Dr Liesel van der Merwe is a small animal medicine specialist. Send her your questions: This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Dr Liesel van der Merwe

The word ‘chemotherapy’ means treating something with chemicals to get a positive result. By this definition all medicines fall under this classification as all medicines are chemical compounds. However, the general usage of the term implies the treatment of cancer with very strong anticancer drugs.

Chemotherapeutic agents are broadly divided into five groups, depending on their source and basic mechanism of action. All cells undergo proliferation, called mitosis. During this phase DNA is duplicated and the identical pairs of chromosomes thus created are pulled to each pole of the original cell and two new cells are created.

All normal tissues have on/off switches which determine how often they proliferate. The cells lining the intestine and the bone marrow cells proliferate very rapidly, whereas mature nerve cells do not proliferate at all under normal circumstances. In cancer cells this on/off switch is either not working or is ignored.

The chemotherapy agent generally targets the cell when it is in the process of dividing. This means that cancer cells, which divide frequently, are good targets. But chemotherapy is non-specific; it targets any dividing cell. Other rapidly dividing tissues in the body are also affected and this accounts for the side effects of chemotherapy.

By using combinations of chemotherapies from different groups with different mechanisms, our chances of killing off more cancer cells increases. This is why combination treatments are sometimes more effective than single drug treatments. Research has, however, shown that certain cancers are more susceptible to certain specific agents. Treatment has to be specifically designed for the patient, the cancer, the risk of side effects and the availability of medications. 

Surgically removing cancer is the best option, but some cancers cannot be surgically removed or are of the bone marrow (such as leukaemia and lymphoma) and need to be treated with drugs or radiation. Combinations of all three modalities are often used.

Most people have negative associations with chemotherapy and don’t want this option for their pets.

The dosages and regimens we use in animals are not as strong as those used in people as we cannot manage the side effects and perform bone marrow transplants as easily. Most animals may be nauseous for one to two days after chemotherapy and the long haired dogs may lose their long coats.

The bone marrow function is checked by doing a full blood count at the time of the expected maximum side effects of the drug and this determines future doses. Cost could be an obstacle and the courses are time intensive, sometimes requiring weekly initial treatments, but most even out at a treatment every third week. The courses might take up to six months.

Radiation is indicated postoperatively in some tumours that couldn’t be completely removed, as well as in bone cancer where radiation can be an important form of pain control.

The treatment is not as efficient as it is in humans because we cannot split up the treatment. People undergoing radiation treatment usually get a small daily dose of their treatment for six weeks. Due to lack of veterinary facilities and a required anaesthesia, most animals get the whole dose divided into four weekly treatments.
This is less effective over the long term and can have more side effects. Immediate short-term radiation side effects that are common in people and cause a great deal of discomfort, such as oral ulcers and skin inflammation, are actually rare in pets.

So, if your pet has cancer, you need to weigh up long term prognosis of the type of cancer, invasiveness of treatment, quality of life during and after treatment and the cost of the treatment in both time and money. Each case needs to be decided on its own merits.

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