Elevated serum levels of PTHrP are found in ˜80% of patients with solid tumors and hypercalcemia.16,24,25,26,27 and 28,30,30a PTHrP levels are almost always elevated in patients with hypercalcemia in the absence of bone metastasis (humoral hypercalcemia) and in solid tumors with squamous histologic features.16,58 PTHrP secretion by tumor tissue should precede the development of hypercalcemia. Indeed, PTHrP elevations can be detected in a small percentage of cancer patients when they are still normocalcemic.16,59