Immunohistochemistry in detection of paraneoplastic secretion of calcium regulating hormones

29 non-endocrine tumors with clinical suspicion of paraneoplastic hypercalcemia were examined using immunohistochemistry specific for PTH and CT. In 19 of these cases intracellular immunoprecipitates have been demonstrable thus showing the paraneoplastic production of peptide hormones (18 PTH, 1 CT). Four of these tumors have been tested in tissue culture for in vitro production of endocrine active substances. In all cases the incubation medium yielded a positive reaction for PTH. The use of immunocytochemistry in the differential diagnosis of hypercalcemia in tumor patients is discussed.