Mar 05 2008

Cancer in pets


Our pets have changed dramatically in the past fifty years. They have gone from working animals to companions and have moved from the backyard to our beds. Our pets also are living longer with this change in lifestyle and improved veterinary care. One consequence of this longevity has been an increase in age-related diseases. In future months, we will discuss some of these in detail. This month, we will explore one of scariest diseases and one that pet owners dread to hear about their pet- cancer.

The term cancer encompasses a large number of diseases. It occurs when cells in the body no longer stop multiplying. It can occur with essentially any cell in the body and can have devastating results. Some cancers result in lumps, others cause inappropriate amounts of hormones to be produced, still others affect the function of the internal organs, and unfortunately, some can be life-threatening.
dog_examDiagnosing cancer can involve many different types of tests. Many times, we will find a problem during the physical exam. Things like lumps on the body or in the mouth, weight loss, masses in the abdomen or pain along bones can indicate cancer. An abnormal finding on an exam may lead to further testing such as blood tests, radiographs and ultrasound. Very often, a biopsy may be done. This involves surgically taking a sample of the abnormal tissue and sending it to a pathologist for evaluation.

Once we find out what type of cancer is present, we can decide the best course of action for treatment. Many types of cancer are treatable with chemotherapy. One of the most common types we treat with chemotherapy is lymphoma. Lymphoma is one of the most common cancers in dogs and cats. In dogs, some of the signs are enlarged lymph nodes, weight loss and excessive drinking and urinating. Cats may also have enlarged lymph nodes and also can show signs related to the digestive tract (diarrhea, vomiting), liver or kidneys. Cats that have feline leukemia virus are predisposed to getting lymphoma, therefore it is always a good idea to make sure your cat has been tested negative.

Other common tumors we see in dogs are on or in their skin. Luckily, many of these are benign, which means they do not spread (or metastasize). The treatment for them is surgical removal and biopsy. If the mass is something that our doctors feel should be removed, it is always a good idea to have it biopsied because some good and bad tumors look very similar to the naked eye. If it is a type that may be dangerous to your pet, we would then discuss further treatment options.

Large breed dogs are particularly prone to bone cancer (known as osteosarcoma). The first sign is lameness and pain when the affected area of bone is squeezed. Also in large breed dogs, hemagiosarcoma, a cancer that most commonly affects the spleen and/or heart, is prevalent. Both of these are serious cancers and treatment can involve surgery and possibly chemotherapy.

Female dogs and cats that are not spayed early (ideally before the first or second heat cycle), commonly develop breast (or mammary) cancer when they are older. Studies have shown that dogs that have been spayed prior to their first heat cycle have an incidence of breast cancer of essentially zero (0). Any nodule associated with the mammary glands should be evaluated. In dogs, they are benign 50% of the time and so removing the lump cures them, but the other 50% are malignant and the sooner they are removed, the better the prognosis. In cats, mammary tumors are malignant 90% of the time, so early treatment is essential. Dogs and cats spayed before the first heat cycle have a 95% decreased risk of mammary cancer.

There are many options now for treating pets with cancer. Increased research about pet cancers has resulted in new methods including surgery, chemotherapy, radiation and immunotherapy (use of vaccines and other immune-modulating drugs). The first step, however, is diagnosis, so if you have any concerns about a lump your pet has or if you feel that he is not doing well for any reason, bring him in for an exam and we will make a treatment plan that is best for your pet.

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