In a multi-institutional series of 49 thyroid medullary carcinomas, cytological specimens (including 29 primary tumors and 20 metastases), and 20 control thyroid gland carcinomas and secondary tumors, 93.75% of medullary carcinomas revealed INSM1 nuclear positivity including all primary tumors showing a sensitivity of 92.3% and a specificity of 100% to discriminate medullary carcinoma from other thyroid malignancies [24]. This evidence concerns the gene INSM1 and medullary thyroid gland carcinoma.