A dog with a perineal tumor and hypercalcemia most likely has which type of tumor?

• A. Transitional cell carcinoma
• B. Squamous cell carcinoma
• C. Apocrine gland adenocarcinoma (anal sac)
• D. Hemangioma

Answer: (C)

A perineal mass with high calcium in a dog points strongly to an anal sac origin because this tumor, the apocrine gland adenocarcinoma of the anal sac, commonly produces parathyroid hormone–related protein (PTHrP). PTHrP causes humoral hypercalcemia by stimulating calcium release from bone and increasing renal calcium reabsorption, leading to the observed hypercalcemia and related signs such as Pu/Pd and weakness. This association makes anal sac adenocarcinoma the best explanation for both the location of the tumor and the systemic calcium disturbance. The other tumors listed do not have the same well-known link to hypercalcemia.