PARATHYROID-HORMONE (PTH)-RELATED PROTEIN, PTH, AND 1,25-DIHYDROXYVITAMIN-D IN DOGS WITH CANCER-ASSOCIATED HYPERCALCEMIA

Circulating N-terminal PTH-related protein (PTHrP), N-terminal PTH, and 1,25-dihydroxyvitamin D [ 1,25-(OH)2D] concentrations were measured in normal dogs and dogs with cancer-associated hypercalcemia (CAH), parathyroid adenomas, and miscellaneous tumors. PTHrP was undetectable (<1.8 pM) in normal dogs and increased in dogs with CAH due to adenocarcinomas derived from apocrine glands of the anal sac (44.9 +/- 27 pM), lymphoma (8.3 +/- 4.4 pM), and miscellaneous carcinomas (13.3 +/- 11.4 pM). The PTHrP concentration decreased in dogs with lymphoma and anal sac adenocarcinomas after successful treatment of CAH. The PTHrP concentration had a significant linear correlation with total serum calcium in dogs with anal sac adenocarcinomas and hypercalcemia, but not in dogs with lymphoma and hypercalcemia. Serum N-terminal PTH concentrations were usually in the normal range (12-34 pg/ml) for all groups of dogs except dogs with parathyroid adenomas (83 +/- 38 pg/ml). The serum PTH concentration increased after successful treatment of CAH. Serum 1,25-(OH)2D concentrations were decreased, normal, or increased in dogs with CAH, and 1,25-(OH)2D levels decreased after treatment of CAH. In summary, circulating concentrations of PTHrP are consistently increased in dogs with CAH, and PTHrP appears to play an important role in the induction of hypercalcemia.