I remember one of my grandmother’s farm dogs suffering from massive breast tumors. But I wasn’t aware until years later while working as a vet tech that pet breast cancer is common. And deadly.
October is National Breast Cancer Awareness Month for humans, and it’s also National Pet Wellness Month. I doubt that anyone in today’s world hasn’t been touched by this disease either personally or by knowing someone who has.
But did you know cats and dogs get pet breast cancer? And some of the research for people helps cats and dogs–and vice versa.

Toy and Miniature Poodles have a higher risk of breast cancer than some other breeds.
Cats & Dogs Affected by Pet Breast Cancer
Pet breast cancer accounts for half of the cases of canine cancer, and about 50 percent of canine breast tumors are malignant. High-risk breeds include the Poodle, English Spaniel, Cocker Spaniel, English Setter, German Shepherds, Maltese and Yorkshire Terriers, while low-risk breeds for mammary cancer include the Boxer and Chihuahua.
The older the dog, the greater the risk of tumors. Most canine mammary tumors occur in unspayed dogs more than 10 years old. It’s less common in dogs younger than five.
Cats & Pet Breast Cancer
Breast cancer is not as common in cats as in dogs, but it’s more deadly in felines. Nearly 90 percent of feline breast tumors are malignant. Male cats and dogs almost never get mammary cancer.
The cause of pet breast cancer remains unknown. However, because it affects certain breeds more commonly, genetics are thought to play a role. Recent research indicates that certain genes are overexpressed in dogs with this condition.
You can learn more about cancers, diagnosis and treatments in my aging pet books, Complete Care for Your Aging Dog or Complete Care for Your Aging Cat.

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EARLY SIGNS OF BREAST PROBLEMS
In almost all cases, you will find the lump or bump on your cat or dog while petting her. Breast exams, particularly for older female cats and dogs, are a great idea because they can detect lumps and bumps very early. Survival time depends on the size of the tumor when first treated. The smaller the tumor when treated, the better the chance your pet will do well.
Therefore, it’s extremely important to have your veterinarian evaluate potential problems immediately. Never settle for a “wait and see” approach—that gives cancer more time to grow and spread, and reduces the chance of a good treatment outcome. Isn’t it better to find out that your dog’s lump was nothing to worry about than to discover too late that it’s cancer and no longer treatable?
BREAST CANCER TREATMENT IN PETS
The standard treatment for mammary tumors is surgical mastectomy (removal) of the affected glands. That may be a single breast or multiple breasts (usually) on one side of the abdomen. Your regular veterinarian may be able to perform this surgery, or you may wish to contact a veterinary oncologist.
Holistic pet therapy also can help, often in conjunction with conventional treatments. Sometimes chemotherapy is suggested in addition to the surgery if not all of the tumor can be removed and/or if it has already spread. Some veterinary cancer specialists recommend using chemotherapy first to help shrink the tumor before it is surgically removed.
Please remember that cats and dogs don’t lose their hair, and rarely feel sick during chemotherapy treatment. Pets don’t even know they’re sick, so they don’t become upset just at the mention of the “C-WORD” that fills people with terror.

Siamese cats have a higher incidence of pet breast cancer than other cats.
Preventing Pet Breast Cancer–YES, YOU CAN!
Unlike some other cancers where a roll of the dice seems to decide who will be affected, mammary cancer can be prevented—or the risk drastically reduced—in our pets. Spaying female dogs before their first heat cycle will nearly eliminate the risk. Intact (un-spayed) dogs will have seven times greater chance of developing mammary cancer.
Cats benefit from spaying prior to first heat, too, and spaying before 6 months gives cats 91 percent lower risk compared to unaltered cats. There’s still a benefit to spaying up until two years (about 11 percent less risk), but if you wait any longer the incidence of mammary tumors is the same as unaltered cats. Siamese cats have two times greater risk of developing breast cancer than other cats and at a younger age. Add breast checks to your happy healthy cat month checklist.
Belly Rubs for Health!
Cancer tends to be a disease of aging pets. Starting this month, I hope everyone will pay more attention to their cats and dogs, starting with breast exams. I promise, your pet will thank you for the extra tummy rub.
Have your pets been touched by cancer? Often I’m told the dogs and cats who go through this prove to be inspirational to their human families, living in the moment and still finding joy despite health challenges. What advice would you offer pet lovers who must face such trials? Do tell!
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Amy Shojai, CABC is a certified cat & dog behavior consultant, a consultant to the pet industry, and the award-winning author of 35+ pet-centric books and Thrillers with Bite! Oh, and she loves bling!
I recently lost my cat (Kitty) to mammary cancer. Treatment wasn’t a option since it was discovered too late. She kept by me as usual for naps. She nearly stopped eating except for her favorite tuna treats which I let her pig out on. For the most part she acted like there was nothing wrong. The cancer soon took to her lungs too. After 1.5 months, she walked in the room and just collapsed to the floor having very difficulty breathing. Like most people, I panicked….but badly. She didn’t make it to the 24hr emergency vet.
The guilt I had for waiting too long was expected but when I panicked I wasn’t even thinking and that guilt hit much harder. I also was at a bad spot in life and was nearly broke. Ended up calling 2 24hr emergency vets. Also for some people who don’t know, like me, don’t stop at your human ER. I was driving by so I figured I’d call and ask.
Nothing can ever prepare you for events like this but having a plan set is the best anyone can do. Kitty’s vet was thrilled to know that I got her to eat and wanted to see her in a couple days. About 6 hours later she had passed. I got her thru a PetSmart adoption event and she was terrified being there. I couldn’t let her pass having the same feeling. She has impacted my life more than I realized, helped me get through some tough times. She was much too young at 10 years of age but I’m glad I got to be her human for those years.
One thing I’d like to advise other pet parents is to start looking into aftercare options. Talk to your vet about at home euthanasia. It would be lot easier if I spent more time on finding that stuff out beforehand.
I’m so sorry for your loss. Thanks for sharing your story and your advice.
Wow! Who knew? I hadn’t realized, for sure. Thanks for the info!