Although relatively uncommon, carcinoma of the apocrine glands of canine anal sacs is highly invasive, metastatic, and associated with paraneoplastic syndrome of hypercalcemia. This retrospective study characterized the signalment, clinical signs, and biological behavior of anal sac carcinoma in 113 dogs. Previous studies have reported that these tumors primarily occur in older female dogs; however, in this study, the sex distribution was almost equal (54% female, 46% male). The tumors were often an incidental finding, with only 61% of the dogs having noticeable perianal swelling. Hypercalcemia was found in 29 (27%) of the dogs. Several treatment methods, including surgery, radiation, and chemotherapy, were used. Median survival time of treated dogs in this study was 544 days (~18 months), which is better than previous reports of 6 to 8.3 months. If the tumor was larger than 10 cm2 at diagnosis or had metastasized to the lungs, survival time was significantly shorter.
COMMENTARY: Carcinoma of the apocrine glands of the anal sac appears to be much more common in males than previously thought. Since the outcomes (survival time) were significantly better in dogs with smaller tumors, rectal palpation, including evaluation of the anal sacs, should be a routine part of the physical examination in all dogs to detect occult disease. Even though metastatic and mortality rates are high, the results of this study imply that early aggressive therapy improves survival times.
Carcinoma of the apocrine glands of the anal sac in dogs: 113 cases (1985-1995). Williams LE, Gliatto JM, Dodge RK, et al. JAVMA 223:825-831, 2003.