Apocrine gland anal sac adenocarcinoma
The second most common cause of hypercalcemia of malignancy in dogs
In dogs, apocrine gland anal sac adenocarcinomas are the second most common neoplastic cause of hypercalcemia of malignancy.1 The secretion of pthrp by carcinoma cells is generally the cause of calcium elevations.1-3 It is reported that 25% to 51% of dogs with apocrine gland anal sac adenocarcinomas are hypercalcemic,4-6 and the identification of elevated calcium concentrations at diagnosis has been inconsistently associated with shorter survival
times.4,5
Given the relatively high incidence of serum calcium elevations in patients with apocrine gland anal sac adenocarcinoma, a
careful rectal examination should be an integral part of the physical examination in dogs with hypercalcemia (see figure). Primary anal sac tumors may be small, so thorough and careful palpation of the anal sacs may be necessary for tumor detection.
In addition, because it is not uncommon for apocrine gland anal sac adenocarcinomas to have regional metastatic disease in
the iliac lymph nodes that may be much larger than the primary tumor, abdominal ultrasonography with special attention to
the sublumbar area is recommended when an anal sac mass is palpated or in cases of hypercalcemia of unknown origin.
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A transverse computed tomography image of a 9-year-old male neutered Siberian husky demonstrating a contrast-enhancing mass
(arrowheads) originating from the right anal sac area and extending in the pelvic canal, pushing the rectum (arrow) laterally toward
the left. This dog was treated with multimodality therapy consisting of surgical excision of the primary tumor and regional
lymph nodes, followed by megavoltage radiation therapy and systemic chemotherapy. The dog was lost to follow-up more than
two years later. Hypercalcemia rapidly resolved after supportive therapy and surgical excision of the primary and regional
metastatic lesions.
REFERENCES
1. Rosol TJ, Nagode LA, Couto CG, et al. Parathyroid hormone (PTH)-related protein, PTH, and 1,25-dihydroxyvitamin D in dogs
with cancer-associated hypercalcemia. Endocrinology 1992;131:1157-1164.
2. Morrison WB. Paraneoplastic syndromes and the tumors that cause them. In: Morrison WB. Cancer in dogs and cats: medical and surgical management. 2nd ed. Jackson, Wyo: Teton NewMedia, 2002;731-735.
3. Grone A, Weckmann MT, Blomme EA, et al. Dependence of humoral hypercalcemia of malignancy on parathyroid hormone-related
protein expression in the canine anal sac apocrine gland adenocarcinoma (CAC-8) nude mouse model. Vet Pathol 1998;35:344-351.
4. Williams LE, Gliatto JM, Dodge RK, et al. Carcinoma of the apocrine glands of the anal sac in dogs: 113 cases (1985-1995).
J Am Vet Med Assoc 2003;223:825-831.
5. Bennett PF, DeNicola DB, Bonney P, et al. Canine anal sac adenocarcinomas: clinical presentation and response to therapy.
J Vet Intern Med 2002;16:100-104.
6. Rosol TJ, Capen CC, Danks JA, et al. Identification of parathyroid hormone-related protein in canine apocrine adenocarcinoma
of the anal sac. Vet Pathol 1990;27:89-95.
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