If your female dog hasn't been spayed by the time she reaches ten years old, canine mammary tumors are a danger. Toy and miniature poodles, spaniels, and German shepherds seem to be the most susceptible breeds. When one or more tumors develop, there's roughly an equal chance of their being benign or malignant. In either case, they should be surgically removed immediately. Early detection and treatment give the best chances for recovery. Examine your dog regularly and see your vet if you detect any unusual lumps or swellings. The best way to prevent mammary tumors is to have your dog spayed before her first or second heat. This will significantly decrease your pet's chances of developing tumors later in life.