Hypercalcemia of malignancy in a dog with cutaneous apocrine gland carcinoma and malignant myoepithelioma

Humoral Hypercalcemia of Malignancy (HHM) is a commonly reported condition in dogs affected by several cancers, mostly T-cell lymphoma and anal sac gland carcinomas, but also other type of tumors. We report the case of a 6-years-old, female neutered Border Collie with an ulcered nodule on the right retromandibular region, that had mild serum total calcium elevation (14,1 mg/dl; reference range (RR): 8,4 to 11 mg/dl) in the absence of clinicopathological abnormalities or imaging finding suggesting any known cause of hypercalcemia. Histologically, the tumor had a tubular epithelial component, admixed with a second, dominant, myoepithelial one; immunohistochemically, the former strongly reacted with anti-Cytokeratin antibodies, while the latter had a weak and patchy immunoreactivity both to Cytokeratin and a-SMA, while Vimentin and Calponin immunostaining was strong and diffuse, suggesting the diagnosis of apocrine gland carcinoma and malignant myoepithelioma. After the excision of the tumor, calcium decreased within limits (8.8 mg/dl RR: 8.4 to 11. mg/dl). In the author's knowledge, this is the first report of HHM associated with apocrine sweat gland carcinoma in the dog.