Medullary thyroid carcinoma (MTC) occurs as a part of multiple endocrine neoplasia (MEN) type 2. Acromegaly, a pituitary adenoma, occurs as a part of MEN1. Rarely, MEN2 and MEN1 coexist in a single patient simultaneously. A 40-year-old man with a history of pituitary adenomectomy for acromegaly had a surgical resection of thyroid carcinoma clinically diagnosed as MTC. His mother, who had MTC and pheochromocytoma, had a germline mutation in the RET gene that could cause the subtype, MEN2A. Identification of gene mutations in RET and MEN1 were examined in the subject. The resected tumor was pathologically diagnosed as MTC. Genomic examinations revealed the RET mutation C634F, which was identical to the mutation of his mother, but no MEN1 gene mutation was found. Although the simultaneous occurrence of both MEN2A and sporadic acromegaly may be accidental, there is evidence to suggest a genetic interaction between MEN2 and acromegaly.
