We report a case of multiple: endocrine neoplasia type 2B (MEN 2B) with de nova RET proto-oncogene mutation, The patient, a 23-year-old Taiwanese woman, was admitted for treatment of recurrent medullary thyroid cancer (MTC) 7 years after a total thyroidectomy. Mucosal neuromas and marfanoid appearance were also noted. Because MEN 2B was suspected, the patient and her family members underwent genetic analysis, A heterozygous germline mutation at codon 918 (ATG --> ACG) of the proto-oncogene RET was detected in the patient. This mutation was considered de novo, as it was not detected in either of her parents or her siblings. he patient underwent surgery for removal of the recurrent tumor. Although no pheochromocytoma was noted, regular follow-up is necessary because of persistent hypercalcitoninemia.
