Abstract
Multiple endocrine neoplasia type 2 (MEN2) is autosomal dominantly inherited disease characterized by medullary thyroid carcinoma (MTC), pheochromocytoma and primary hyperparathyroidism. MEN2 is divided into three clinical subtypes; 2A, 2B and FMTC (familial medullary thyroid carcinoma). The causative gene for MEN2 is RET oncogene located on chromosome 10q11.2. In RET gene analysis, exons 10, 11, 13–16 should be analysed. More than 98% of MEN2 patients had RET germline mutation. RET gene testing is strongly recommended for all patients with MTC because RET mutation is discovered in approximately 10–15% of patients with apparently sporadic MTC. In Japan, RET gene testing can be performed under health insurance system since April 2016.
RET gene testing can discriminate relatives with mutation from those without mutation. So, prophylactic total thyroidectomy for children with RET mutation can be performed. The narrow definition of prophylactic total thyroidectomy is that total resection of the normal thyroid gland before the development of MTC in children. Therapeutic early total thyroidectomy for children with micro MTC or C-cell hyperplasia should be distinguished from prophylactic total thyroidectomy (narrow definition). In Japan, prophylactic total thyroidectomy (narrow definition) for children has not been performed because of the limitation of health insurance system. However, prophylactic or therapeutic early total thyroidectomy without severe complication such as recurrent laryngeal nerve palsy and permanent hypoparathyroidism should be widely accepted in Japan.
