Medullary thyroid carcinoma and other rare types of thyroid carcinoma

Among 4 major traditional groups of thyroid carcinoma, papillary and follicular carcinomas are most common, and other forms, anaplastic and medullary carcinomas, are relatively rare. The 2003 WHO histological classification of thyroid tumor separated 7 other malignant thyroid tumors into distinct pathological entities, such as poorly differentiated, squamous cell, mucinous carcinomas, carcinoma showing thymus-like differentiation (CASTLE), etc. Although they are also extremely rare, recognition of their clinicopathologic features are very important. In this review, not only diagnostic and therapeutic strategies for the rare forms of thyroid carcinomas, specifically focussed on medullary carcinoma and CASTLE, but also their histogenetic abnormalities were discussed.