In the course of follow-up of two patients who presented with prolactin-secreting pituitary adenomas, we encountered an unemphasized sequel: the evolution of multiple extrapituitary neoplasms of endocrine-gland origin. Tumors were either present concurrently or evolved sequentially. The pedigree of one family was affected in an autosomal dominant manner with tumors of the pituitary, parathyroid glands and pancreatic islet cells, documenting with the most extensive kindred to date the association of prolactinoma with multiple endocrine neoplasia I. These cases, in conjunction with ultrastructural histopathology of three other multiple endocrine neoplasia I prolactinomas, and review of the literature, delineate the following considerations: (1) a prolactin-secreting pituitary adenoma may be the first manifestation of multiple endocrine neoplasia I, with concurrent or sequential tumor evolution; (2) the occurrence of endocrine tumors in these families is sporadic or conforms to a heritable pattern of autosomal dominance; (3) the ultrastructural morphology of prolactinomas in multiple endocrine neoplasia I cannot be used a priori to identify patients at risk for multiple endocrine neoplasia I from those with randomly occurring, isolated prolactinomas; (4) thus, we recommend serum calcium determinations and a detailed family history with inventory of endocrine systems in all patients with prolactinoma; (5) in identified families with the multiple endocrine neoplasia I syndrome, serum prolactin concentrations should be determined; and (6) the cost effectiveness of extensive biochemical screening for multiple endocrine neoplasia I in patients with prolactinoma without an incriminating family history will require further clarification.
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