1Meet Kimber. She is an 11-year-old Great Pyrenees dog who was brought to Blue Door Veterinary Services to have some large lumps on her mammary chains examined. Her owner noticed the first lump about a year ago, which slowly got bigger and bigger. The second lump developed a few months ago and seemed to grow quickly after her last heat cycle in the spring. Both masses were each the size of a cantaloupe when she came to see us.


Mammary gland tumors are very common in dogs, so Kimber is not alone in her condition. Luckily, about half of mammary tumors are benign, but the only way to know for sure is to remove them for a biopsy. Smaller samples of the tumor may not be enough to determine if it is benign or malignant. If the dog has multiple tumors, they could all be different, so each one should be removed and biopsied separately.


Because of the size of the tumors, aggressive surgery to remove large parts of her mammary chain around the masses was necessary. We performed two separate surgeries for Kimber, as each mass was so large, it took about 3.5 hours to remove each one. To keep her under anesthesia any longer for each surgery could have been unsafe for her.

Kimber may have been able to avoid these surgeries if she had been spayed when she was younger. Research has shown that spaying dogs before their first or second heat cycle can dramatically reduce their risk of developing mammary gland tumors.


The prognosis for dogs with benign mammary tumors is good after surgical removal. For dogs with malignant mammary tumors, the prognosis depends on multiple factors: tumor type, size, regional lymph node involvement, presence or absence of metastases in other organs, and completeness of surgical resection are some of the considerations. In general, for any type of cancer, the best prognosis is related to early detection and treatment.

In comparison to our canine companions, cats have a much higher incidence of malignant tumors on the mammary glands. About 85% of mammary lumps in cats are malignant compared to the 50% in dogs. Prognosis for cats with mammary tumors is directly related to the size of the mass and the length of time it has been around, so prompt treatment is of utmost importance.

If you see any lumps anywhere on your pet, call us today to schedule an appointment for us to evaluate the masses and determine the safest and best course of action for your furry family member.


Kimber recovered after her second surgery – no more huge masses!