CMTM6 and cancer: CMTM1–8 are known tumor suppressor genes (Bu et al., 2008; Li et al., 2011, 2015; Liu et al., 2013, 2015; Xie et al., 2014; Zhang et al., 2014, 2016; Gao et al., 2015; Xiao et al., 2015; Bei et al., 2017; Choi et al., 2018; Huang et al., 2019; Zhu et al., 2019); in addition, CMTM6 is a key regulator of PD-L1 in various human cancer cells.