PTH and Hypercalcemia: Many tumors (breast, lung, kidney, squamous carcinomas) secrete PTHrP, which mimics PTH to drive bone resorption and hypercalcemia (81).A recent meta-analysis found that PHPT patients have a 28% higher overall cancer risk, with papillary thyroid and breast cancers being the most common (82).The mechanism may involve PTH/PTHrP’s effects on cell proliferation and altered vitamin D/calcium metabolism.