Hypocalcemia associated with estrogen therapy for metastatic adenocarcinoma of the prostate.

We report 2 cases of true hypocalcemia (not caused by decreased binding proteins) associated with metastatic prostate cancer and review previously reported cases. Hypocalcemia is a common but frequently unrecognized complication of prostatic cancer. Estrogen therapy often is associated with the hypocalcemia, which may be asymptomatic. The hypocalcemia is always associated with osteoblastic metastases and usually it is associated with increased serum alkaline phosphatase activity, acid phosphatase activity and serum parathyroid hormone concentration. Serum concentrations of magnesium, phosphorus and vitamin D frequently are decreased. Patients are in a positive calcium balance. The osteoblastic metastases seem to act as a calcium sink, creating a "hungry tumor phenomenon". The role of estrogens may be to stop the resorption of normal bone resulting in lower serum calcium concentrations.