Ectopic production of intact parathyroid hormone by a squamous cell lung carcinoma in vivo and in vitro

Ectopic tumoral production of intact parathyroid hormone (PTH) is rare. The PTH-related protein is the common cause of hypercalcemia in most solid tumors, particularly squamous and renal carcinomas. We report the case of a 71-yr-old man with a PTH-producing squamous cell lung carcinoma. Immunocytochemical analysis of the tumor tissue as well as of cultured tumor cells revealed PTH positive staining. Cultured tumor cells released PTH and were calcium sensitive, producing 122 +/- 16 pg/mu g DNA of intact PTH (mean +/- SEM) at 0.5 mmol/L calcium compared with 26 +/- 2 pg/mu g DNA at 3.0 mmol/L calcium. Somatostatin analogues have been used in the treatment of humoral hypercalcemia of malignancy (HHM). However, we found that somatostatin (0.1 mu g/L) in cultured tumor cells increased the release of intact PTH (123 +/- 19 versus 82 +/- 1 pg/mu g DNA, P < 0.05) and thus might have a negative effect on the HHM. This report is the first to describe a true ectopic PTH-producing squamous cell lung carcinoma associated with HHM.