Q Someone told me I should be giving my dog regular breast exams to check for cancer. That’s patently ridiculous — right?
Portsmouth, New Hampshire
Dear Ms. Lemmer,
A It’s not at all ridiculous to give your dog breast exams if she was not spayed before her first heat. A dog spayed before her first heat has virtually no chance of ending up with mammary (breast) cancer. But her risk rises substantially if spaying occurs after the first heat. And any potential cancer-sparing benefit may be lost completely after the third or fourth heat.
It’s a good idea to give an older female dog (say, eight years or older) who was not spayed before her first heat mammary exams every four months or so. You want to be feeling for unexpected lumps or bumps. Don’t just check the nipple and right below it. Palpate the whole surrounding area, feeling carefully beneath the skin.
Keep in mind that there are 10 “breasts,” that is, five pairs of mammary glands, and they go quite far back, essentially to a dog’s hind legs. And it’s the two pairs of glands toward the back that are most likely to end up with mammary tumors.
If you do find even a very small growth on any of the glands, take your dog to the vet. Even small masses that turn out to be benign should be removed; there is some evidence that they could become malignant.
The standard treatment is surgery, sometimes followed up by chemotherapy if the tumor is large, or has spread to lymph nodes or lungs or invaded blood vessels or the lymphatic system.
Note that with mammary cancer, there’s a 50/50/50 rule. Out of 100 dogs with a bump in a mammary gland, 50 percent will have malignancies. Of that 50 percent, 50 percent will spread to other body tissues and ultimately prove fatal. To simplify the math, 25 percent of bumps found in dogs’ mammary glands turn out to be fatal. The ones that are not are usually small tumors that have not yet spread. That should put the value of canine “breast exams” into context.