Parathyroid hormone-related protein as a cause of hypercalcemia in a B-cell type malignant lymphoma.

Hypercalcemia occurred in a patient with non-Hodgkin's (B-cell type) lymphoma when generalized lymphadenopathy developed. Despite low normal plasma parathyroid hormone (PTH), nephrogenous cAMP (NcAMP) was not suppressed, and serum and urine PTH-related protein (PTH-rP) levels were elevated. The plasma level of 1,25(OH)2D was within normal range. The combined chemotherapies successfully reduced the tumor size, serum Ca, PTH-rP, and lactic dehydrogenase. Serum osteocalcin was suppressed while the patient was hypercalcemic, and increased after chemotherapy. In the extract of the tumor tissue obtained post mortem, bioactivity stimulating the production of cAMP in osteoblasts was demonstrated along with the immunoreactive PTH-rP. This is the first report of a B-cell lymphoma producing PTH-rP and its association with humoral hypercalcemia of malignancy.