Mammary Gland Cancer In Dogs and Cats

Mammary Gland Cancer is a common form of cancer for dogs and cats who have had at least 2 heat cycles before being spayed. It appears as one or many nodules on the underside of your dog or cat that is associated with the mammary gland underneath the nipple. In the following article, I will discuss mammary gland associated cancers, the differences between this cancer in dogs and cats, how to prevent your pet from getting this disease, and treatment options available.

Mammary Gland Adenocarcinoma is the term given for cancer associated with the mammary gland. It is divided into many sub-types which are classified as benign or malignant tumors. Benign tumors are unlikely to spread to other tissue whereas malignant tumors do have the potential to spread to other areas and tissues. While the exact appearance of mammary tumors can vary, many nodules will feel like hard, irregular growths associated with the mammary gland. They may be red, swollen, and painful and they may grow becoming infected and rupture, leaking a pus-like, bloody discharge.

There are several factors which affect the prevalence of mammary cancer in dogs and cats. Spaying and obesity appear to be two of the most important factors. Dogs who are spayed before their first heat cycle have less than a 0.5% chance of acquiring mammary cancer compared to intact female dogs. The risks increase with the number of heat cycles and dogs and cats who have gone into heat twice may have a cancer rate as high as 25% – meaning 1 in every 4! In addition, breed and genetics may play a role in disease incidence as well as obesity early in life.

It is important to note at this time that approximately 50% of mammary tumors in dogs are cancerous. Meaning half are benign and not dangerous and half are malignant/cancerous. In cats, unfortunately, the overwhelming majority of mammary tumors are cancerous. To correctly identify cancerous vs. benign tumors, a biopsy is required which can be done as a stand-alone test or as part of the removal of the mass or masses. Aspirates or needles placed into the mass to acquire cells are not diagnostic and cannot differentiate malignant vs. benign growths.  

Surgery is the main treatment option for pets with mammary cancer without evidence that they have spread to other organs. Single tumors may be removed or the entire mammary chain depending on a case by case evaluation. Routine bloodwork and radiographs are recommended prior to surgery to identify signs of cancer elsewhere in the body and to assess the surgical risk to the patient. Other treatment options include radiation therapy, chemotherapy, and anti-inflammatory medications which may help limit the inflammation. They may also improve outcomes and limit associated pain. Studies also suggest the size of the tumor can predict outcomes; with smaller tumors having better long term outcomes than larger tumors.

An ounce of prevention is worth a pound of cure. For this and many other reasons, it is recommended to Spay your female dogs and cats before their first heat cycle. While there is a long-standing debate about the correct time to spay your pet; spaying at a young age before the first heat cycle will almost entirely eliminate the risk of mammary cancer in your dog or cat. Spaying at about 6 months of age is the most common veterinary recommendation at this time.

Veterinary Hospital For Mammary Gland Cancer

Mammary tumors are painful and many are dangerous, and it’s best to avoid them by spaying early. To find out more about spaying your dog or cat, or if you think your pet may have a mammary tumor, I recommend calling one of our offices to schedule an appointment with a member of our Veterinary Hospital. With a little information and a lot of love, we’ll help keep your dog’s tail wagging and your cat purring for years to come.

 

Jeffrey Stupine  VMD

Medical Director

World of Animals Veterinary Hospitals