Functioning oxyphil cell adenomas of parathyroid gland: immunoperoxidase evidence of hormonal activity in oxyphil cells.

Functional oxyphil adenomas of parathyroid gland are rare. Several studies have suggested that these tumors consist of a mixed cell population and that the transitional oxyphil cells and/or chief cells are the main source of parathormone, while the fully developed oxyphil cells have minimal or no hormonal activity. This report describes light, ultrastructural, and immunocytochemical features of six parathyroid adenomas, and confirms that these neoplasms are composed of a mixed cell population. It also demonstrates that the oxyphil cells have strong hormonal activity and therefore can play a significant role in the pathogenesis of hyperparathyroidism.