ABCB1 and gastric cancer: Previous studies prove that ABCB1 is a classical ATP-dependent drug efflux pump (Sharom, 2008) and plays key roles in the drug resistance of various tumors, such as gastric cancer (Wu et al., 2018), urothelial cancer (Vallo et al., 2017), lobular breast cancer (Krech et al., 2012), osteosarcoma (Han and Shi, 2018) and so on.