Introduction
Intrathyroid thymic carcinoma (ITTC)/carcinoma showing thymus-like differentiation (CASTLE) is a rare cancer with slow growth which bears histological similarity with thymic carcinomas and clinically shows positive treatment responses 1. Occasionally, ITTC metastasizes into lymph nodes and/or to distant organs, resulting in a poor prognosis 2,3. However, no effective drugs have been developed for controlling metastatic ITTC. Herein, to explore new therapeutic strategies for a metastatic ITTC, we uncovered specific genetic mutation and immune microenvironment profiles in metastatic ITTC by next-generation sequencing (NGS), multiplex immunohistochemistry and imaging cytometry.