While most rectal tumors are inside the bowels and are not visible, an initial sign of anal gland cancer in a canine is a mass near the anus. Female dogs are equally vulnerable to anal gland or sac tumors. Certain breeds, including German shepherds, springer and cocker spaniels, malamutes and dachshunds, have higher rates of anal gland carcinoma.
Tumors of the anal sacs (apocrine gland adenocarcinoma is the most common tumor type) are a serious but uncommon problem because they tend to invade surrounding tissues and metastasize (spread to distant tissues) even when the primary tumor is very small. The tumors are almost always only on one side.
An anal sac adenocarcinoma is an uncommon and aggressive malignant tumor found in dogs that arises from the apocrine glandular tissue of anal sac. The disease exists in cats as well, but is much less common in that species. [1