Hypercalcemia and parathyroid hormone-related peptide expression in a dog with thyroid carcinoma and histiocytic sarcoma

A 9.5-year-old, male castrated Walker Hound was presented for evaluation of progressive weakness, anorexia, and weight loss. Imaging revealed multiple abdominal and thoracic masses and ascites; fine-needle aspirates of mesenteric and splenic masses confirmed malignancy, most likely histiocytic sarcoma. Laboratory analyses revealed increased ionized calcium and parathyroid hormone-related peptide (PTH-rP) concentrations, and concurrent low-normal parathyroid hormone concentration, consistent with humoral hypercalcemia of malignancy. Necropsy was performed after euthanasia. The dog had disseminated histiocytic sarcoma, including sarcomatosis, as well as bilateral thyroid carcinoma. PTH-rP immunostaining was positive in the thyroid carcinoma but negative in the histiocytic neoplasm. These results suggest that thyroid carcinoma-associated hypercalcemia can be caused by tumor secretion of PTH-rP.