Using a sensitive radioimmunoassay,we detected human immunoreactive calcitonin in cell extracts and in cell-exposed media of the HL60 cell line derived originally from a patient with acute promyelocytic leukemia. The cell extract was chromatographed on a reverse-phase high- pressure liquid chromatography system. Radioimmunoassay of the fractions showed that the immunoreactive calcitonin was heterogeneous but had peaks corresponding to those of synthetic human calcitonin monomer and its sulphoxide. We have previously shown that levels of immunoreactive calcitonin are elevated in the plasma of the majority of patients with acute and chronic myeloid leukemias. Our studies with the HL60 cell line add further support to the concept that leukemic cells can synthesize immunoreactive calcitonin “ectopically.”

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