Familial non-multiple endocrine neoplasia medullary thyroid carcinoma: Report of a case confirming a new clinical entity in Japan

Most hereditary medullary thyroid carcinomas (MTC) occur in association with multiple endocrine neoplasia (MEN) type 2 syndromes. Since Farndon et al. reported two kindreds, that is collections of relatives, with familial non-MEN MTC in 1986, only five kindreds with this disorder have been reported in the English literature. In this paper, we describe a rare Japanese kindred with familial non-MEN MTC, confirming the existence of this distinct clinical entity in Japan. A 42-year-old woman underwent a left hemithyroidectomy with modified neck dissection (MND) under a diagnosis of sporadic MTC at 28 years of age. She developed lymph node metastasis in the right neck region 7 years after the initial surgery, and underwent MND and right hemithyroidectomy. Although no findings of MTC were histologically confirmed in the resected right thyroid lobe, C-cell hyperplasia was observed. Hereditary MTC was strongly suspected, but we could not confirm specific manifestations associated with MEN type 2 in any family members. However, 7 years later, a paternal aunt and cousin were diagnosed with MTC. Other family members were evaluated by ultrasonography and calcium-pentagastrin provocation testing, and three additional patients with MTC across two generations were found. None of these patients had any extrathyroidal manifestations associated with MEN type 2, and the entity of familial non-MEN MTC was confirmed.