CLDN6 and gastric cancer: CLDN6 is expressed in pluripotent stem cells and fetal tissues but repressed in most adult tissues (Ben-David et al., 2013; Kong et al., 2021; Reinhard et al., 2020), whereas CLDN6 is overexpressed in 54–100% of germ cell tumors, 14–55% of ovarian cancers, 17–21% of endometrial cancers, 10–52% of gastric cancers and 6–11% of NSCLCs (Du et al., 2021; Micke et al., 2014; Qu et al., 2021; Zhang C. et al., 2021).