If your veterinarian isn't already giving your dog routine rectal exams, ask your vet to do so.  An ounce of prevention might make the difference between treatable and terminal cancer.  Apocrine gland adenocarcinoma--cancer of the anal sacs--is an aggressive cancer that typically metastasizes into the lymph nodes.  These tumors typically occur in older female dogs (10+), but unneutered male dogs are also at risk for the disease. The anal sacs surround the last inch of the gastrointestinal tract.  Once the tumor forms, it usually grows larger and larger until it compresses the rectal area, causing the dog to have difficulty evacuating its bowels.  Routine rectal exams are important because, unfortunately, by the time owners see a primary symptom of the cancer--the dog straining during a bowel movement--the disease has usually progressed to a point where diagnosis and treatment options are limited and very expensive. Most veterinarians will refer the case to a surgical speciality center if the owner wishes to battle the disease.  A biopsy (removing a piece of the tumor for examination) is performed while the dog is under sedation.  Once the diagnosis is confirmed, surgery may be an option if the tumor isn't too large.  The surgery is invasive with a painful recovery, often leaving the dog incontinent--a big decision to make, especially for an older pet.  This type of tumor tends to recur, so multiple surgeries may be required.  Radiation and chemotherapy are also treatment options and can be used in combination with surgery or palliatively if the tumor cannot be surgically removed.