Pets Can Get Breast Cancer Too

By: Elizabeth Fowler, DVM

TVMA Member
New Braunfels, TX

Published July 2015

Thanks to awareness campaigns such as October’s Breast Cancer Awareness Month, the dangers of breast cancer and the life-saving benefits of early detection have become widespread knowledge. However, mammary or breast cancer in our pets gets much less publicity.

Did you know that dogs and cats get breast, or mammary, cancer too? Mammary cancer is actually the most common tumor in female dogs and the third most common tumor in female cats. In intact female dogs, the risk of mammary tumor development is 26 percent. This is three times the risk of breast tumors in women. In dogs, there is approximately a 50-percent chance that the tumor will be malignantA medical condition that will become progressively worse.. In cats, that risk is even higher at 80 percent to 90 percent.

How is Breast Cancer Detected?

When you are petting your pets, it’s always good to be aware of any lumps or bumps that you may feel. Remember that dogs and cats have multiple “breasts,” or mammary glands that lie over the abdominal muscles. On average, they have 10 mammary glands—five on each side—extending from their chest to their groin. The first sign of breast cancer in a pet is typically a painless lump or mass. It may be large or small and may have distinct boundaries or not. Some lumps are freely movable while others are fixed and adhere to the underlying tissues. Occasionally the mass may ulcerate and bleed. Some may cause secretions from the nipple.

If you find a mass, you should make an appointment to be seen by your veterinarian for a complete examination. The first step in treatment is to determine what type of mass is present. This information can be gained by a surgical biopsy and submission of tissues to the lab for evaluation. This will determine if the mass is benign (not likely to metastasizeTo spread to other sites in the body by metastasis.) or malignant (likely to metastasizeTo spread to other sites in the body by metastasis.). If it is malignant, there are additional tests and treatments that will be recommended. X-rays can determine if the tumor has already spread to other parts of the body. Cancerous tumors can spread quickly. Most often they secondarily affect the pelvic lymph nodes and the lungs. Spaying will be recommended with any tumor type to reduce the stimulation provided by hormones and hopefully slow future tumor development. Depending on the type of tumor chemotherapy, radiation and immunotherapy may be suggested as well.

How Can Breast Cancer be Prevented in Pets?

Prevention is always the best medicine. If a dog is spayed before her first heat cycle, her risk of breast cancer is reduced to less than 1 percent. Prior to her second heat cycle, her risk is still only 8 percent. After the second heat cycle, there is no significant impact on her risk by spaying. There are similar benefits to spaying cats early. Dogs will experience their first heat cycles when they reach puberty, which is usually around the age of six months but will vary depending on breed. Typically, smaller breeds will experience their first cycles at a younger age than their larger counterparts. Intervals between cycles will vary by breed, but the average is about once or twice a year.

In human medicine, it is widely accepted that preventative wellness programs reduce the effects and costs of serious illnesses and increase the effectiveness of treatments. The same is true in veterinary medicine. On average, our pets age three years every six months. It is important to schedule regular wellness exams for our pets every six months and have them examined for lumps and bumps as well as for many other things that can help extend the length and quality of our pets’ lives. Early detection is essential to positive outcomes for treatment.

Elizabeth Fowler, DVM, lives in New Braunfels, Texas. Dr. Fowler practices at County Line Veterinary Clinic.