Bone metastases and tumor-induced hypercalcemia.

Tumor-induced hypercalcemia and tumor-induced osteolysis are essentially due to a marked increase in osteoclast-mediated bone resorption, although the kidneys play an important contributory role in the genesis of tumor-induced hypercalcemia. Parathyroid hormone-like protein plays an essential role in tumor-induced hypercalcemia, and maybe in tumor-induced osteolysis, but other factors could also be responsible for the osteoclast activation secondary to the neoplastic infiltration of the skeleton. Treatment of tumor-induced hypercalcemia essentially consists of volume repletion and administration of potent anti-osteolytic drugs. The bisphosphonate pamidronate is particularly useful for that matter and a dose of 1.0 to 1.5 mg/kg can normalize serum calcium in about 90% of hypercalcemic cancer patients. The apparently low response rate of bone metastases to systemic antineoplastic therapy seems to essentially reflect the relative insensitivity of our current methods for assessing response in tumor-induced osteolysis. Newly developed biochemical markers of bone turnover could be particularly useful for that matter. Bisphosphonates are the most potent of the available inhibitors of osteoclast activity. Prolonged administration of oral pamidronate could reduce by almost one half the complications of tumor-induced osteolysis, and repeated bisphosphonate infusions could induce a dramatic relief of bone pain in one third and a sclerosis of lytic lesions in one fourth of the cases. These data must, however, be confirmed in randomized, blinded trials and many questions remain unanswered concerning the optimal therapeutic schemes. Medical therapy of tumor-induced osteolysis by noncytotoxic means has nevertheless become a reality.