Sunday, May 6, 2007

Coping With Cancer in Pets

PREVIOUSLY this column has discussed various age-related problems that dogs and cats can develop -- all of which have corresponding conditions in humans: kidney failure, heart disease, etc.

Probably the most dreaded word in medicine -- cancer -- happens to all animals as well. While usually something that happens later in life, cancer tragically can occur at any age.

It is important to realize, however, that cancer is not a single disease, but rather a class of diseases. There are different possible ways to treat these conditions based on what kind of cancer is present, so it is important for a doctor or veterinarian to arrive at a specific diagnosis before deciding on whether to recommend treatment.
For example, some cancers can be removed completely by doing surgery. Of course, in some instances this can be as extreme as an amputation, which may or may not be a realistic option for some pets.

Some cancers, like lymphoma, that occur throughout the body, are not treatable with surgery, but can be treated with medications (chemotherapy). And it's important to remember that not all chemotherapeutic drugs are the same. Some are oral or injectable medications with minimal side effects, whereas others can have severe side effects.

Different drugs are used in various combinations for different kinds of cancer. For some types, a single drug can be given by mouth once a month. This is probably the simplest form of chemotherapy. For other types of cancer, a combination of injectable, oral, and IV drugs is used.

The side effects of chemotherapy usually involve suppression of the immune system and an upset intestinal system.

The reason these systems are involved pertains to the mechanism by which most chemotherapy drugs kill cancer cells. Chemotherapeutic medications work by killing a cell at the time it divides into two cells. For cancer, where the cells are constantly dividing out of control, the cells are susceptible to these drugs.

However, the immune cells in the body (white blood cells) and cells that line the digestive tract are constantly being destroyed in the body, and the remaining cells are constantly reproducing and dividing to replace those that are being lost.

When these cells are exposed to chemotherapy they are killed like the cancer cells. One difference between most dogs and cats, compared with humans, is that pets rarely lose any fur.

The reason for this is that the cells at the base of a human hair are constantly dividing which is what makes our hair grow, whereas in cats and most breeds of dogs very few of the hairs are actually growing at any given point in time.

A few breeds like poodles and Old English sheepdogs will lose their fur while on chemotherapy, and cats will sometimes lose their whiskers. As with humans, the fur grows back when the medications are discontinued.

For other types of cancer, radiation can be effective. Radiation therapy generally involves exposing the area of the tumor to radiation repeatedly over a period of several weeks. One recent advancement in the treatment of lymphoma in dogs involves administering two radiation treatments in addition to a routine chemotherapy protocol.

The field of veterinary oncology continues to advance in step with research into treatments for different kinds of human cancer. And just as there are specialists in human medicine (oncologists) who only deal with cancer and its treatment, so there are veterinary oncologists.

However, even though treatments exist for various cancers in pets, a judgment call must always be made regarding the appropriateness of treating a particular pet.

If a pet is very old, or the chances of remission are low, then we usually recommend against treatment. If, however, a pet is otherwise healthy and the chances of remission are excellent, we often recommend treatment.

At our practice we do a significant amount of surgery and chemotherapy to treat cancer in pets, but always discuss the pros and cons of these options with a pet owner.

Ultimately, it is their decision to treat or not to treat. Our aim is to support a pet owner to what ever extent we can, whether it is in their decision to employ the most advanced treatments for their pet's cancer, or to let them live out their life as comfortably as possible without major intervention.

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