He is the soul of honesty and loyalty, and is never false or treacherous even in his old age. — 1938 AKC Boxer breed standard. The breed is particularly predisposed to mast cell tumours, a cancer of the immune system. Median lifespan was 10.25 years. Responsible breeders use available tests to screen their breeding stock before breeding, and in some cases throughout the life of the dog, in an attempt to minimize the occurrence of these diseases in future generations.