October is Breast Cancer Awareness Month. Many pet owners may not be aware that dogs and cats can also get breast cancer, referred to as mammary cancer. Although it is rarer in cats, 25 percent of all unspayed female dogs will develop mammary tumors, according to the American College of Veterinary Surgeons (ACVS).
Fortunately, mammary cancer is easy to prevent – and it’s another reason why spaying or neutering your pet is so important. Mammary cancer rarely occurs in male dogs or in female dogs and cats that have been spayed. Mammary tumors, on the other hand, are the most common type of tumors found in female dogs that were never spayed or were spayed after the age of two.
“Dogs spayed before their first heat cycle have only a .5 percent risk, or virtually no risk, of developing mammary cancer,” writes Dr. Ken Tudor on petsMD.com. “The risk increases to 8 percent when spayed after the second heat. By 2.5 years of age, spaying offers no decreased risk benefit. This argues for early spaying, since mammary tumors are very common.”
Why is mammary cancer more common in dogs that have not been spayed? Every time female dogs go into heat, their bodies endure a 60-day hormonal pregnancy, regardless of whether or not they actually breed. (This can cause a condition known as false pregnancy, where a dog believes she is going to have puppies, and starts lactating and nesting.)
The dog breeds most at risk for mammary cancer, according to the ACVS, are poodles, dachshunds and spaniels. For cats, it’s Siamese or other Oriental breeds, and domestic short hairs. Young dogs that are obese also have a higher risk.
Mammary tumors can be small and benign, or large growths that can spread to the lungs. About half of the ones found in dogs are cancerous, which is comparable to the ratio of malignant breast tumors found in women. Mammary cancer in dogs is rarely fatal. But for cats, about 85 percent of tumors are malignant, and they tend to be more aggressive and spread more quickly through the cat’s body.
As with breast cancer, mammary cancer can often be successfully treated if it’s detected early. Just like performing a monthly breast exam, pet owners can regularly check their dogs and cats for any suspicious new lumps or growths by palpating the mammary glands.
“When tumors first appear, they will feel like small pieces of pea gravel just under the skin,” writes Race Foster, DVM, on peteducation.com. “They are very hard and are difficult to move around under the skin. They can grow rapidly in a short period of time, doubling their size every month or so.”
If you see or feel anything out of the ordinary, you should immediately take your pet to a veterinarian.
As with other types of canine and feline cancers, veterinarians usually diagnose mammary cancer on the basis of the pet’s medical history and a physical exam. According to the ACVS, your vet may want to run additional tests, such as X-rays, blood tests and ultrasounds to confirm the diagnosis. A biopsy of the mammary tissue is usually necessary to help determine if the tumor is malignant.
Unless the dog or cat is very old, surgical removal of the tumor is usually recommended. If surgery on malignant tumors is performed early enough, the cancer can be completely eradicated in half of the cases.
In some cases, the mammary glands must be removed — but this is nothing like a radical mastectomy in humans. The surgery is easier and the recovery time is faster. “In humans, this type of surgery would affect the underlying muscle tissue, which complicates the recovery,” Dr. Foster explains. “In the dog, however, all of the breast tissue and the related lymphatics are outside of the muscle layer, so we only need to cut through the skin and the mammary tissue.”
For cats, the local lymph node may also be removed to see if the cancer is spreading.
Chemotherapy is not usually successful in treating mammary cancer, so it is not widely used. “For most mammary tumors in cats and dogs, hormonal therapy, immunotherapy and radiation therapy have either not been investigated or aren’t beneficial,” adds the ACVS.
While dogs may live for several years after surgery, the prognosis for cats is not as positive, according to the ACVS. Depending on the size and spread of the mammary tumor, cats may live from just a few months to a few years after surgery.
Not much can be done to prevent many cancers in pets, but mammary cancer is the exception. In fact, Dr. Foster notes that if all female dogs and cats were spayed before their first heat cycle, mammary cancer “could be almost completely eliminated.”
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