Cat Breast Cancer: What You Need to Know

Breast cancer is ranked as the number one most heavily funded area of cancer research in people, according to Cancer.org, yet cat breast cancer has failed to gather much attention in the world of feline health. Despite this common tumor being such an uncommon topic, as noted by Merck Veterinary Manual, around 90% of mammary tumors in cats are malignant. Much like breast cancer in people, breast cancer in cats is prone to spreading to the patient's lungs and lymph nodes. Read up on this dangerous cancer in cats.

Clinical Signs of Cat Breast Cancer

The most commonly observed physical clue pointing toward breast cancer in cats is indeed a growing mass along the breast tissue chain on the cat's chest and abdomen. Masses may be isolated, all located on one side or seem to be randomly distributed. Unfortunately, by the time many pet parents notice it, the cancer may have spread to internal organs. Beyond lumps or swollen tissue, breast cancer in cats can also appear as:

• Skin rash on the breast tissue
• Reddened, painful skin
• Swollen tissue that may be bleeding or seeping discharge
• Ulcerated tissue
• Black and necrotic tissue

While we don't fully understand why some cats develop breast cancer and others do not, we do know that hormones contribute significantly to the development of mammary tumors in cats. This is why most veterinarians recommend spaying your cat before their first heat cycle. Some cats are believed to have a greater susceptibility to cancers due to genetics.

Cat Breast Cancer Risk Factors

Because hormones play a role in the development of breast tumors, the more a cat is exposed to those hormones, the higher their chances are of developing them. This puts middle-aged to older animals at the highest risk to develop cat breast cancer, though breast tumors can occur in younger cats, as well.

While no breed is immune, vets see much more breast cancer in Siamese and Persian cats, as compared to domestic short-haired cats. Mammary tumors are rare in male cats, but do occur, contrary to popular belief.

Diagnosing Cat Breast Cancer

Dr. Margaret McEntee, a professor of Veterinary Oncology at Cornell University's College of Veterinary Medicine, explains, "a cat has two 'chains' of four mammary glands and nipples running parallel on each side of its belly." It is along this mammary chain that breast cancer is found in the cat. The tumor often starts so small it is easily missed by even the most attentive pet parents. The mass is most often located just beneath or next to one of the nipples, though anywhere along the breast chain or incorporated surrounding tissue is possible.

To move forward with a diagnosis, your vet may recommend two outpatient diagnostic tests: radiographs (X‑rays) and tissue samples (biopsies). These allow the vet to avoid confusing mammary tumors with non-dangerous overgrowth of mammary tissue, called mammary hypertrophy. While nursing, cats may also develop swollen breast tissue for other reasons, including mastitis, an infection of the breast tissue, or a clogged milk duct. If you see any abnormal swelling, its best to contact your veterinarian.

Prognosis of Cat Breast Cancer

Breast tumors in cats are staged to help your vet estimate your cat's prognosis, as well as determine the best treatment. A simplified look at staging involves tumor size and regional and distant spread.

Tumor size is the single most important prognostic factor, as explained by experts at The Ohio State University Veterinary Medical Center. Cats with larger tumors have the shortest survival time (around four to six months), while cats with tumors smaller than a 2 cm diameter have a median survival time of over three years.

Evaluating regional lymph nodes is useful in telling the vet if the tumor has spread locally. While you can't evaluate every cell of the lymph node, if your vet notices a change in size of lymph nodes, that's generally a good sign. Lymph node size increase is usually an exaggerated change, and not the typical subtle increase in size because of mammary adenocarcinoma, the most commonly diagnosed breast tumor in cats.

Distant metastasis is the final category your vet will use to evaluate the tumor and your cat's prognosis. In order to gauge if distant metastasis has occurred, your vet will evaluate the lungs by reviewing chest radiographs (X-rays). The lungs are a common site for distant spread.

Treatment and Prevention of Cat Breast Cancer

According to The Ohio State University Veterinary Medical Center, surgery is the go-to choice for mammary tumors in cats. Radical mastectomy, which is the removal of all glands on the affected mammary chain side, significantly reduces the chance that the tumor will come back. Your vet or a veterinary oncologist will work with you to determine the best surgery for your cat.

Chemotherapy is also often used alongside surgery. Cats generally experience fewer and less severe side effects from chemotherapy than humans because a gentler dose and less intense schedule is typically used in cats. While cats may sometimes experience an upset stomach from chemotherapy, they usually do not experience hair loss like people do.

While cat breast cancer is a real threat to felines of all ages, breeds and even genders, the great news is that spaying your cat at a young age is an easy and effective method of prevention. Spaying your cat before the first heat cycle is ideal, as it provides the greatest protection against the effects of hormones. Talk to your vet about the best course of treatment for your favorite furry friend.