Q:At my 13-year-old cat’s recent yearly checkup, a new mammary growth was found. The veterinarian said it is producing milk and will continue to grow. He put a sample under a microscope and thinks it is benign but can’t be sure. Is surgery the right course?
A:Thanks for getting in touch, and I very much understand your concern for your girl. I think there are a number of things to consider in close consultation with your veterinarian, and I am hopeful that by working together you can devise a plan that will provide the best outcomes with respect to her quality of life and prognosis.
While the possibility of mastitis (inflammation of the mammary gland with or without bacterial infection) exists, this is most commonly diagnosed in cats that are lactating, so unless this kitty is nursing kittens (not likely), I think mastitis is less likely the cause of this mass. I will presume that your kitty is spayed, but if she is not, the possibility of reproductive hormones playing a role in the development of this mass is something to consider.
Another possibility is a condition called feline mammary hypertrophy (fibroadenoma). This is a benign, rapid growth of the cells that line the mammary glands that can occur in intact (i.e., not spayed) older female cats, usually one to two weeks after their heat cycle. Again, when seen in older female cats, they are usually not spayed, and ovariectomy (removal of the ovaries) is almost always curative and usually prevents recurrence. Mastectomy is also curative, but recurrence may occur if a cat is intact.
The last and most potentially serious possibility is a mammary tumor (i.e., cancer). About 90% of feline mammary tumors are malignant adenocarcinomas, and they most commonly occur in intact females over the age of 11 years.
The prognosis for these tumors depends largely upon their size at diagnosis, evidence (or lack thereof) of spread to regional lymph nodes, the presence (or absence) of metastasis to the lungs and other organs, and their rate of growth.
Importantly, cats that are diagnosed with mammary adenocarcinomas that are 2 cm in diameter or smaller have a median survival time of over 4 years, while those diagnosed with mammary adenocarcinomas that are 3 cm or more in diameter have a median survival time of six months. This highlights the importance of making these diagnoses as early as possible.
Therapies for mammary adenocarcinomas involve surgical removal of the mass alone, the affected mammary gland, the affected mammary gland and all others that share lymphatic drainage, or removal of all mammary glands in the chain of glands on the affected side. The more radical surgical procedures have not, thus far, been proven to provide prolonged survival when compared to the less invasive ones. While still the subject of ongoing research, some chemotherapeutic protocols may be beneficial in cats with mammary adenocarcinomas.
As I hope you can understand, I cannot provide the answer as to whether surgery is the right or wrong option from afar, and it is very important that you continue to work closely with your veterinarian and/or a veterinary oncologist to devise the best diagnostic and therapeutic plan. In the interim, it seems reasonable to me to gather more information, such as thoracic radiographs and an abdominal ultrasound to rule out metastasis to the lungs and/or abdomen; as these may be diagnostically and prognostically helpful.
If there is any doubt as to whether this may be a mammary adenocarcinoma after considering all of these issues, surgical intervention may very well be the best route to pursue, given the potential negative health impacts of untreated mammary adenocarcinomas in cats.
I hope this is helpful, and best of luck to you and your kitty. Please send us an update when you can.
