Dog “Breast Cancer”: Mammary Disease


Dr. Trisha Joyce, a veterinarian for New York City Veterinary Specialists, still remembers the first dog she saw with mammary disease — cancer of the mammary glands. The first dog she saw with mammary disease was brought in for lethargy. “We started off with blood work and X-rays, and the X-rays showed metastatic cancer in her lungs, which had begun in the mammary glands.” Since that time, Joyce has counseled dog owners on how to prevent and detect mammary disease, and how to proceed once it’s been diagnosed.

Risk Factors
Mammary cancer is one of the most common cancers among dogs, but it is also one of the most preventable. “First and foremost, spay your dog,” says Joyce. Dogs spayed before their first heat almost never go on to develop the disease, compared to the 25 percent of unspayed dogs that will. Spaying before a dog’s second heat is almost as protective. Generally speaking, malignant mammary tumors are unusual in dogs spayed before the age of 2.

Mammary tumors are most commonly found in unspayed dogs between 5 and 10 years old. Breeds thought to be at increased risk include Boston terriers, cocker spaniels, poodles, English setters, Brittany spaniels, pointers and fox terriers. Male dogs very rarely develop mammary cancer, though it can happen — and it’s usually aggressive when it does.

When Joyce meets owners of unspayed dogs, she encourages them to perform regular mammary exams at home. The idea is similar to the self-exams that women are taught by their gynecologists to perform in order to become familiar with their own breast tissue. “If you know how your dog’s mammary glands feel when they’re free of tumors, it’s easier to catch a growth if one develops,” she says.

To examine your furry friend, run your hand over the fatty tissue around her nipple. “Just rubbing the belly is too superficial. Squeeze the tissue a little, almost like milking a cow. You’re looking for a lump like a little hard pea, or sometimes bigger,” says Joyce. Finding a lump is a good reason to visit the veterinarian, but it’s not necessarily a cause for alarm. Fifty percent of mammary tumors in dogs are benign.

“If a lump is hard and immobile, I’m more worried than if it’s soft and mobile. But you can never say just by its feel,” says Joyce. Still, other than these telltale lumps, mammary cancer is asymptomatic in its early stages. If it metastasizes, the dog may go on to develop health problems related to where the cancer has spread.

Diagnosis and Prognosis
A biopsy is necessary to determine whether a tumor is benign or malignant, but Joyce says that prompt removal of any mammary tumor is most veterinarians’ treatment of choice, no matter its status. Once the tumor is removed, it can be determined whether it was benign or malignant.

Mammary surgery is less complicated than mastectomy in women, since a dog’s breast tissue is outside of the muscle layer. A dog can be back to its normal activity within a couple of weeks. Prognosis is often good: In 50 percent of cases, the cancer is totally eliminated with the surgical removal of the tumor.

In advanced cancers that have metastasized, surgery may still be performed to reduce the impact of the tumor and improve quality of life. Sometimes, though, a metastasized mammary tumor means it’s time to let your pet go. “The tumors can become ulcerative, making just moving around extremely uncomfortable. Or if they spread to the lungs or the bones and make breathing or walking very hard, the most humane option may be euthanizing,” says Joyce.

Mammary cancer in dogs may be common, but it is preventable and very often even completely curable. With early detection and a relatively easy operation, your dog may be back on its feet in no time, with a chest that is free of problematic lumps.

Rose Springer is a New York City-based freelance writer and frequent contributor to The Dog Daily. She has been writing about pets for a decade.

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