Functional and genetic studies of isolated cells from parathyroid tumors reveal the complex pathogenesis of parathyroid neoplasia.

Parathyroid adenomas (PAs) causing primary hyperparathyroidism (PHPT) are histologically heterogeneous yet have been historically viewed as largely monotypic entities arising from clonal expansion of a single transformed progenitor. Using flow cytometric analysis of resected adenomatous parathyroid glands, we have isolated and characterized chief cells, oxyphil cells, and tumor-infiltrating lymphocytes. The parathyroid chief and oxyphil cells produce parathyroid hormone (PTH), express the calcium-sensing receptor (CASR), and mobilize intracellular calcium in response to CASR activation. Parathyroid tumor infiltrating lymphocytes are T cells by immunophenotyping. Under normocalcemic conditions, oxyphil cells produce ∼50% more PTH than do chief cells, yet display significantly greater PTH suppression and calcium flux response to elevated calcium. In contrast, CASR expression and localization are equivalent in the respective parathyroid cell populations. Analysis of tumor clonality using X-linked inactivation assays in a patient-matched series of intact tumors, preparatively isolated oxyphil and chief cells, and laser-captured microdissected PA specimens demonstrate polyclonality in 5 of 14 cases. These data demonstrate the presence of functionally distinct oxyphil and chief cells within parathyroid primary adenomas and provide evidence that primary PA can arise by both clonal and polyclonal mechanisms. The clonal differences, biochemical activity, and relative abundance of these parathyroid adenoma subpopulations likely reflect distinct mechanisms of disease in PHPT.