One of the joys of cat companionship is petting your feline friend. But beyond its calming effect, frequently running your hand over your cat might end up adding years to her life.

Mammary (or breast) tumors are common in cats, especially un-spayed females 10 to 12 years of age. But sometimes, spayed females and males are affected too — and in about 85 percent of cases, a mammary tumor’s cells can spread to other parts of the body.

Even with therapy, the key factor determining a cat’s prognosis is the mammary tumor’s pretreatment size. After removal of a tumor over 1 inch wide, your cat might live for another four months. But removing a tumor before it reaches three-quarters of an inch might give her another three years of life.

So make use of petting time to check your cat for suspicious lumps.