Significance of parathyroid hormone-related protein as a factor stimulating bone resorption and causing hypercalcemia in myeloma.

Elevated levels of parathyroid hormone-related protein (PTHrP) in hypercalcemic myeloma patients were demonstrated in recent reports, suggesting that PTHrP behaves as a humoral mediator of hypercalcemia in myeloma. Herein we describe a hypercalcemic myeloma patient with a high serum PTHrP level. Moreover, the PTHrP level in the supernatant of bone marrow aspirates was about two-fold of that in serum. Reverve transcriptase-polymerase chain reaction analysis showed PTHrP m-RNA in bone marrow containing myeloma cells. After chemotherapy, the concentrations of calcium and PTHrP decreased and PTHrP mRNA in bone marrow became undetectable. We conclude that PTHrP released by myeloma cells acted as the main bone resorption stimulating factor in this case.