CLDN6 and granular cell tumor: In GCT, carcinoembryonic antigen claudin 6 (CLDN6), a tight junction associated membrane protein may represent an ideal chimeric antigen receptor (CAR) antigen because of its extracellular loop that can be targeted by T cells; moreover, it is silenced during organogenesis, thus is not expressed in healthy cells but only in various cancer cells, including GCT: indeed CLDN6 is expressed in approximately 93% of GCT (47).