Canine Mammory Cancer

If you don't plan to breed your dog, spay her as soon as possible to limit risk of mammary cancer.
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You surely know someone who has been diagnosed with breast cancer. Canine mammary cancer is the equivalent of breast cancer in people. It's the most common type of cancer in unspayed female dogs -- to put it in perspective, the rate of mammary cancer in dogs is three times higher than in people, according to Mammary cancer can affect male dogs, but it's quite rare.

Mammary Cancer

Causes and risk factors for canine mammary cancer vary. Overweight intact female dogs are at higher risk of developing mammary cancer than intact dogs of normal weight. While there's a hereditary component in some people for breast cancer, it's not clear whether that holds true for canines, whether in general or for specific breeds.


Symptoms of mammary cancer generally appear in older dogs, those ages 7 and up. Mammary tumors might change color from the rest of the dog's skin, or even ulcerate. Your dog might or might not appear in pain if you handle any lumps. If you feel a lump along her abdomen in the nipple area, take her to the vet for an examination.


Your vet will take a biopsy of the tumor and send it to a veterinary pathologist, who can determine whether the tumor is malignant or benign. If malignant, or cancerous, further testing reveals how far the tumor has spread. These tests consist of X-rays or ultrasounds of the dog's abdomen. Canine mammary cancer generally spreads, or metastasizes, to the lungs and lymph nodes. The dog's prognosis depends on whether or not her cancer has spread. According to Purdue University, about half of canine mammary tumors have metastasized.


As with any cancer, treatment depends on how far the disease has spread. Tumors, whether benign or malignant, are generally surgically removed. Early-stage cancers, those relatively small tumors that haven't spread, are often cured with surgery. Dogs whose tumors have spread might be treated with chemotherapy or given palliative care to ease pain. Depending on the drug used, chemotherapy can have serious side effects, including heart issues and renal failure.


If you have no intention of breeding your dog, spaying her at an early age almost always prevents the disease from developing. According to the Veterinary Cancer Group, dogs spayed before experiencing their first heat cycle have only a 0.05 percent chance of developing mammary cancer, while dogs spayed after the first heat cycle but before the second have an 8 percent lifetime risk of the disease. Dogs spayed after their second heat cycle have a 26 percent lifetime risk.