Breast Cancer in Dogs and Cats
- posted: Oct. 06, 2024
Breast Cancer in Dogs and Cats
October has long been Breast Cancer Awareness month calling attention to this serious disease affecting 1 out of every 8 women. But did you know, dogs and cats can develop breast or mammary tumors, too? This week’s blog discusses some of the common risk factors, diagnostics, and treatments for mammary tumors.
Mammary tumors in both dogs and cats are much more common in older intact or un-spayed females. Spaying your dog before her first heat cycle greatly reduces the chance of developing mammary tumors as she ages. The chance of a mammary tumor developing in a dog spayed before her first heat is only 0.5%. This risk increases to 8% if spayed after one cycle and jumps to 26% if spayed after the second heat and beyond. Cats have about a 9% chance of developing breast cancer as adults if spayed before 6 months of age and about a 14% chance if spayed after one year of age.
Estrogen influences tumor development which is why spaying-removing the ovaries and uterus-greatly reduces the risk of breast tumors in pets. In fact, dogs have been used as models for human breast cancer as many of “the clinical similarities include the spontaneous tumor incidence, onset age, hormonal etiology and the identical course of the disease. Furthermore, the factors that affect the clinical outcome, including the tumor size, clinical stage and lymph node invasion, are identical.”1
In cats, nearly all mammary tumors are malignant (85% or more) and they often behave aggressively with rapid growth and ulceration and have a tendency to metastasize. In dogs, about half of the mammary tumors diagnosed will be cancerous and half will be benign. Malignant tumors can metastasize, but it seems a bit less common than in cats.
In most cases, a mammary tumor is diagnosed by palpating a lump, or multiple lumps, under the skin in one or more mammary glands on the belly. If a mass is found, the mass may be aspirated for more information or to rule out other tumor types. However, aspirating a mammary mass does not usually provide information as to whether the tumor is malignant or benign. A biopsy of the tissue is needed for exact diagnosis of the type of mammary tumor and whether it is cancerous or not. Mammary tumors are almost always found in older female dogs and cats, over the age of six. Mammary tumors in male dogs and cats are extremely rare.
Surgical removal of all mammary tumors is the treatment of choice and, in many cases, if multiple masses are found, a mastectomy or removal of the entire mammary chain may be needed. It is also recommended to spay the cat or dog if she is not already spayed to reduce estrogen influence and future tumor development. Chest x-rays, bloodwork and examination of regional lymph nodes are usually recommended prior to surgery to determine if metastasis has occurred. Metastatic disease holds a more guarded prognosis.
Cats and dogs with malignant mammary tumors can have adjunct treatment such as chemotherapy. Radiation is less common and less effective. Benign mammary tumors should be cured with surgery and have a good outcome. Malignant tumors hold a guarded prognosis with survival time of anywhere from a month to a year or more depending on the tumor type and whether the cancer has spread to other areas of the body.
Spaying dogs and cats while they are young vastly reduces the risk of breast cancer in our pets. And, if you feel a lump on your cat’s or dog’s belly, especially if she is not spayed and is older than 6 years of age, have your pet examined by a veterinarian. Diagnosis and removal of mammary tumors can improve quality of life and survival time if diagnosed early, especially in dogs.
This blog brought to you by the Patton Veterinary Hospital serving Red Lion, York and the surrounding communities.
1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6004712/
Location
Patton Veterinary Hospital
425 E Broadway
Red Lion, PA 17356
