Plasma parathyroid hormone related-protein levels in patients with cancer, normocalcemic and hypercalcemic

Hypercalcemia in patients with cancer may reflect the synthesis and secretion into circulation of parathyroid hormone-related protein (PTHrP) produced by the tumor. In the present study, we have measured circulating PTHrP concentrations in healthy subjects and patients using a new immunoradiometric assay (IRMA) that is specific for the 1-86 amino acid sequence of molecule, and in plasma collected with protease inhibitors. Plasma concentrations of PTHrP(1-86) were greater than the detection limit of the assay (0.3 pmol/l) in healthy subjects. All patients with hypercalcemia-associated cancer had PTHrP(1-86) levels significantly greater (median 7.74 pmol/l, P < 0.05) than healthy subjects or patients with cancer and normal serum calcium, primary hyperparathyroidism and hyperparathyroidism secondary to chronic renal failure. Plasma PTHrP and corrected serum calcium were correlated in patients with hypercalcemia-associated cancer. In one patient, a marked decrease in PTHrP and calcium levels was observed following surgery. Our results suggest that this IRMA for PTHrP(1-86) may be useful for diagnosis and monitoring of PTHrP-producing tumors induced hypercalcemia.