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What is Cancer?
Cancer is the unrestrained and unregulated growth of cells that occurs despite the body's anticancer defense mechanisms or immune system. Cancer begins with a single cell that fails to respond to growth signals from the rest of the body. This cell can begin to grow undetected for weeks, months, or years before it ever becomes clinically apparent. Cancer is caused by many things, including genetic abnormalities that occur for many reasons such as a breed predilection, tobacco smoke, certain nutrients, radiation, drugs, toxins, viruses, inflammation, pollution, chemicals or any other substance that can damage DNA. In the majority of animal cancers, it is often difficult to pinpoint a specific inciting cause for the development of cancer. Some cancers are more common than others. Lymphoma (click to download description of Lymphoma) in both dogs and cats is the most commonly treated cancer. In dogs cutaneous Mast Cell (click to download description of Mast Cell Tumors) cancer is the most common skin tumor that we see. As more and more research is being compiled for both human and animal cancer, the treatment options and overall prognosis for all species are improving dramatically and rapidly with new developments available in clinical practice almost daily.
Chemotherapy
Chemotherapy drugs are compounds that are toxic to cancer cells. Chemotherapy may be given by intravenous or subcutaneous injection, or orally. Cancer cells generally multiply very rapidly. Most chemotherapy drugs work by damaging the ability of these rapidly growing cells to divide, eventually killing them. There are risks involved with any type of treatment for cancer. Some normal cells will be injured and killed by the chemotherapy drugs. Side effects may be apparent because of these normal cells being killed. However, these side effects are usually outweighed by the benefits of killing the cancer cells. Dogs and cats generally tolerate chemotherapy much better than human patients. The two side effects encountered most commonly in canine and feline patients are toxicity to the gastrointestinal tract, and toxicity to the bone marrow. Normal cells in both of these areas divide very rapidly, so are more susceptible to the toxic effects of the chemotherapy. When the cells lining the gastrointestinal tract are affected, the result may be vomiting or diarrhea. Most patients will experience this side effect at least once or twice during their course of chemotherapy treatment, but the symptoms are usually mild and can be overcome with supportive care at home. When the cells of the bone marrow are affected, the result may be more serious. The precursor cells that produce the white blood cells necessary the fight infection are found in the bone marrow. If these progenitor cells are damaged, the patient’s white blood cell count may drop low enough to result in an increased susceptibility to infections. White blood cell counts of all canine and feline chemotherapy patients are monitored carefully, but rarely a cat or dog receiving chemotherapy will develop a life-threatening systemic infection. The only way to successfully treat these infections is to admit the patient to the hospital, and administer intravenous antibiotics. Hair loss in cats and dogs receiving chemotherapy is usually very minor, with some notable breed exceptions. If you own a poodle, West Highland white terrier, Old English sheepdog, schnauzer, puli, lhasa apso, shih tzu, bichon frise, Yorkshire terrier, maltese, or curly coated terrier such as an Airedale or Welsh terrier, you should expect that your pet will lose a significant amount of hair during the initial stages of chemotherapy. However, the hair that is lost will grow back after your dog’s course of chemotherapy has been completed, or once treatments are being administered less frequently. Cats usually do not lose any hair, although many will lose their whiskers. Some chemotherapy drugs can be extremely irritating to the subcutaneous tissues if they are able to leak outside the vein during injection. Examples include the chemotherapy drugs vincristine, adriamycin and mustargen, and severe inflammation, ulceration, and swelling can occasionally be seen. However, this complication occurs infrequently, because all chemotherapy drugs are carefully administered through butterfly catheters. The length of a particular course of chemotherapy will vary depending on the disease being treated. The most common cancer treated with chemotherapy is lymphoma. Chemotherapy for this disease is often very successful, and owners of cats and dogs with this type of cancer should realistically expect that their pets will need some form of chemotherapy for the rest of their lives. The course of treatment for other types of cancer is usually much shorter, generally 12 to 15 weeks. Finally, it is vital to understand that most cats and dogs receiving chemotherapy have an excellent quality of life both during and after treatment. It is often possible to provide many additional months, or sometimes even years, of happy life with chemotherapy. The vast majority of owners report that they have no regrets about their decision to pursue chemotherapy for their pet.
Clinical Trials—A Working Network of Oncologists
Ongoing Clinical Trials at the Animal Cancer Care Clinic:
- Mast Cell Tumor. The Animal Cancer Care Clinic has been chosen as one of the investigational sites for a new FDA-approved targeted drug therapy for canine mast cell tumor. Enrollment began in December of 2004 with 2 patients still currently enrolled.
- Melanoma. Currently, a vaccine is available for canine melanoma and the Animal Cancer Care Clinic is able to obtain melanoma vaccine for an ongoing clinical trial from the University of Wisconsin and the University of Florida.
Researchers at the Animal Medical Center in New York in conjunction with Memorial Sloan Kettering will also be releasing the most novel of the melanoma vaccines, a DNA vaccine, that is now scheduled for FDA approval in January of 2007.
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