By Dr. Fiona, a veterinarian and blogger for Pets Best Insurance
October is Breast Cancer Awareness month and pink ribbons are everywhere. Breast cancer is a devastating and common disease in humans, but did you know that dogs can get breast cancer too? Veterinarians typically refer to the disease as mammary cancer, since dogs have a mammary chain rather than two breasts like humans. Here are some facts about mammary cancer in dogs:
Mammary cancer is defined as benign or malignant tumors associated with the mammary glands. About 50% of tumors felt in the mammary glands will be malignant, meaning they can spread to regional lymph nodes and other parts of the body, the other 50% are benign. It is impossible to tell which is which just by feeling or looking at the mass.
Which dogs are at risk?
Almost all cases of mammary cancer are seen in female dogs; it is extremely rare in males. Breeds overrepresented include poodles, spaniels, setters, German shepherds, Maltese, Yorkshire terriers and pointers. The disease typically presents in older pets. The median age of onset is about 10 years old, and is uncommon in dogs less than 5 years of age.
Mammary cancer can present as one solitary mass, or multiple masses along the mammary glands (often under the nipples). They can be freely moveable, or fixed to deeper structures, which is usually more worrisome for malignancy.
There are some genes that have been implicated in mammary cancer in dogs, suggesting there is a heritable component. The cancer is thought to be caused by the hormone estrogen. It is generally accepted among experts that spaying a female dog before her first heat cycle, as a puppy, will decrease her risk for developing mammary cancer later in life. In fact, a dog allowed to have just 2 heat cycles will have a 26% increased risk over a dog that has been spayed as a puppy.
Prompt surgical removal (mastectomy) is the treatment of choice. Your veterinarian will probably recommend radiographs of the chest to ensure there hasn’t already been a spread of the cancer.
Chemotherapy can be considered, although this is infrequently recommended.
Always have the tumor submitted for biopsy so you can be assured the surgeon removed it all, and determine whether or not it is malignant.
Dogs that are still intact should be spayed at the same time as the mastectomy.
Prognosis for recovery and long term survival is good if treated promptly. The biopsy report will tell you which type of cancer (if malignant) the pet had, and some are more serious and aggressive than others. Malignant tumors left too long have a greater chance of having metastasized, which will decrease the pet’s chance of long term survival.
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