Hypercalcaemia in association with Sertoli cell tumour in a dog

A 9-year-old, presumed male castrated mixed breed dog was evaluated for lethargy, hyporexia, polyuria, polydipsia and diffuse gynaecomastia. Bloodwork revealed severe hypercalcaemia and hyposthenuria. CT scan showed a caudal abdominal mass consistent with a Sertoli cell tumour on cytology. Diffuse, nodular mammary gland enlargement was consistent with mammary gland hyperplasia on cytology. A malignancy panel was inconsistent with hyperparathyroidism and showed a normal PTHrP. Abdominal exploratory laparotomy, abdominal mass resections and right chain mammectomy were performed. Sertoli cell tumour and mammary gland hyperplasia were confirmed via histopathology. Hypercalcaemia decreased to within normal range and gynaecomastia in the left mammary chain resolved postoperatively. To the authors' knowledge, this is the first case report of hypercalcaemia associated with Sertoli cell tumour in a dog. While several mechanisms have been proposed for hypercalcaemia of malignancy, the mechanism is unclear in this case.