There are certain tumors that are stimulated to grow by the male hormone, testosterone. An example of this in the male is the tumor that exists around the anal area called the perianal adenoma or carcinoma. They are usually found in the older dog, in multiples, and at various depths within the anal tissues.
Most owners are not aware of this tumor until it has either reached a considerable size or begins to bleed. When this tumor reaches the surface and stretches the skin too tight, a split occurs in the top layer, allowing the tumor to bleed. At this point, odor from infection is usually detected by the owner as well.
Treatment involves removing the growths and submitting a section for biopsy interpretation, removing the hormone stimulus (castration), and treating with antibiotics. While there still remains the possibility for even a benign tumor to return after the castration has been performed it is much less likely than if castration is not performed. In any case good observation on the part of the pet owner is always of benefit to both.