Hepatoid Thymic Carcinoma in a Polycythemia Vera Patient Treated with Ropeginterferon Alfa-2b: Clinical, Histopathological and Molecular Correlates

Hepatoid thymic carcinoma (HTC) is an extremely rare variant of primary epithelial tumor of the thymus morphologically resembling hepatocellular carcinoma Herein, we report an additional case of HTC diagnosed in a 40-years-old man affected by polycythemia vera and treated with ropeginterferon alfa 2-b, for the first time deeply analyzing the molecular profile of this distinctive thymic malignancy. By immunohistochemistry, tumor cells were positive for cytokeratin 7-19, GLUT1, and Hep-Par-1, whereas AFP tested negative. Whole exome sequencing revealed loss of function mutations in TP53, STK11, PBRM1, SMAD3, FN1, NTRK1, and FANCD2, as well as gain of function mutations in MTOR, BCL11A and COL1A1, along with amplification of CCND3 and MDM2. This mutational landscape halfway between thymic carcinoma (TP53, PBRM1) and hepatoid variant carcinoma of other sites (STK11) suggests that, at some point during carcinogenesis, a switch occurred from an epithelial thymic phenotype to a hepatoid-like one.