SLC22A5 and esophageal cancer: Conversely, the DNA topoisomerase II inhibitor etoposide, which is a substrate of OCTN2 and showed some encouraging results in the treatment of esophageal cancer, might be part of novel rationally designed therapeutic regimens to add to the current treatment arsenal against esophageal carcinoma (Kok et al., 1988; Ohwada et al., 1995; Kok et al., 1996; Hu et al., 2012; Tamai, 2013; Yamamoto et al., 2018).