Thyroid-Like Cholangiocarcinoma: Histopathological, Immunohistochemical, In-Situ Hybridization and Molecular Studies on an Uncommon Emerging Entity.

Thyroid-like cholangiocarcinoma is a very uncommon variant of peripheral-type cholangiocarcinoma. To date, only 4 prior cases have been reported. The molecular features of this tumor have not been described. We report a case of a 60-year-old woman with a tumor that evolved over a period of 10 years. A left hepatectomy specimen showed an 11 cm tumor that on histology exhibited areas reminiscent of a thyroid tumor with follicular and insular features which were positive on immunohistochemistry for cytokeratin 7 and in-situ hybridization for albumin. A detailed molecular analysis failed to show mutations common to cholangiocarcinomas but revealed frameshift mutations in 2 chromatin-remodeling genes, CREBBP and KMNT2A. This case confirms that thyroid-like cholangiocarcinoma is a histologic variant of this tumor that is associated with relatively low growth. As most cholangiocarcinomas, it is diffusely positive for cytokeratin 7 and albumin by in-situ hybridization. Given its rarity, the molecular alterations in this specific histologic subtype remain to be fully elucidated.