Representing a crucial factor during cell adhesion, polarity, proliferation and migration, the transmembrane protein claudin 6 (CLDN6) has been shown to be a putative target for the treatment of germ cell tumors (GCT). Particularly seminoma (SE), embryonal carcinoma (EC), and choriocarcinoma (CC) indicated high CLDN6 levels, while about 60 % of yolk-sac tumors (YST) presented as CLDN6+. In this study, we generated CLDN6-deficient GCT cells by CRISPR/Cas9 for SE, EC, and CC cells, while YST cells were cell sorted for CLDN6+ and CLDN6- populations. Further, the putative function of CLDN6 was investigated on proteome level using liquid-chromatography coupled with mass spectrometry (LS-MS).