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Mammary Cancer in Cats
Veterinary & Aquatic Services Department, Drs. Foster & Smith
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Mammary cancer occurs much less frequently in cats than dogs, but when it does occur, it is often malignant and difficult to treat. Mammary cancer is the third most common cancer in cats. Mammary cancer is likely to strike 1 in 4,000 cats. While this is about half the rate as in dogs, when cats develop mammary cancer it is often fatal. There is a strong correlation between early spaying and a reduced incidence of the disease. If mammary cancer is caught early, the treatment is more often successful. This article will help familiarize the cat owner with appearance and treatment of this deadly cancer.

Which cats are at risk for developing mammary cancer?

Any adult female cat can develop mammary cancer, but the average age is usually 10-14 years of age. Siamese cats appear to have a genetic predisposition for developing mammary cancer and are twice as likely to develop it as other breeds. Unspayed females are at a much greater risk of developing mammary cancer. Female cats that were spayed after having one to several heat cycles, with or without having kittens, are also at a greater risk than a cat that was spayed before her first heat cycle. Although rare, mammary cancer can occur in male cats.

What are the types of mammary cancer in cats?

Studies reveal that 85% of mammary tumors in cats are malignant adenocarcinomas. The tumors that make up the other 15% include duct papillomas, sarcomas, and adenomas. Adenocarcinomas are very aggressive tumors and often metastasize to the surrounding lymph nodes and lungs.

What are the symptoms of mammary tumors in cats?

Breast Cancer
Mammary tumors in cats often appear as firm nodules that are moveable or firmly attached to the skin and/or underlying muscle. About one fourth of the tumors are ulcerated. The tumors are more common on the first front sets of mammary glands. In half of the cases, tumors are present in more than one gland. Swelling, pain, infection, and fever may also be present.

What is the treatment?

Treatment usually consists of surgical removal of the tumor and the surrounding mammary gland. Some surgeons recommend complete removal of the entire mammary gland chain. These tumors are extremely aggressive and because of the high incidence of metastasis with adenocarcinomas, an aggressive treatment approach is necessary. Proper identification of the removed tumor is always recommended to help determine if further treatments are necessary. Chemotherapy is often used in combination with surgical removal to increase survivability rates. Because of the technical expertise needed to properly administer the newest and most effective chemotherapy drugs, a consultation with a boarded veterinary oncologist is recommended.

What is the prognosis for cats with mammary cancer?

While the initial treatment for cats with mammary cancer may be successful, the long-term outcome is usually guarded. Up to 65% of surgically removed tumors will reoccur within a year. Unfortunately, most cats survive less than a year after initial diagnosis. However, cats who receive aggressive treatment on small tumors that are caught early may live 2 to 3 years.

How is mammary cancer prevented?

While mammary cancer in cats is not completely preventable, there are several precautions owners can take to decrease the incidence of this disease. The first is to make sure their cats are spayed before they come into their first heat. There is a strong correlation between early spaying and a reduction in the incidence of mammary tumors in cats.

The second precaution is to avoid the use of progesterone-like drugs, which can increase the incidence of mammary cancer in cats. These drugs are still occasionally used to treat miliary dermatitis and some behavior disorders in cats. Owners of female cats need to weigh the risk versus the potential benefits of using these drugs in their cats.

Finally, owners should be sure their cats get regular, thorough veterinary checkups. Owners can perform their own mini checkups by feeling for any lumps or bumps, particularly in the mammary area. Early detection and treatment is very important in the successful treatment and outcome of mammary cancer in cats.

References and Further Reading

Wypij, J; Fan, TM. Malignant mammary tumors: Biologic behavior, prognostic factors and therapeutic approach in cats. Veterinary Medicine. 2006; June:352-364.

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