Failure of indomethacin to reduce hypercalcemia in patients with breast cancer.

Prostaglandin synthetase inhibitors have, in the past, been shown to inhibit osteolysis caused by breast carcinoma tissue in vitro. We therefore assessed the effect of Indomethacin and aspirin on some parameters of calcium metabolism in patients with breast cancer. Neither drug reduced the serum calcium in pateints with hypercalcemia, nor reduced skeletal destruction as measured by the urinary hydroxy proline: creatinine ratio and urinary calcium in normocalcemic or hypercalcemic patients with osteolytic metastases. A possible reason for the discrepancy between results obtained in vitro and in vivo is that there are two phases of bone destruction in breast cancer; the early phase dependent and the late phase independent of prostaglandin synthesis.