Dogs spayed after 2.5 years of age have no decreased risk of breast cancer as compared to unspayed females. I personally have never diagnosed a case of breast cancer in a dog that was spayed before one year of age. Spaying at the same time as tumor removal does not decrease the dog's chance for recurrence of the disease. However, it does eliminate her chances of developing other illnesses that affect older unspayed dogs such as pyometra. If the dog is in good health otherwise and can tolerate the increased anesthetic and surgical time, then spaying can be considered at the time of tumor removal.
Mammary tumors occur commonly in older, intact female dogs.
By doing this, you are also acting as a responsible pet owner, helping decrease the pet overpopulation crisis. There really is no excuse for not following through with this basic responsibility of pet ownership. Do the right thing. Dr. Wayman's biography is available online. All Rights Reserved.