ABCG2 and gastric cancer: It was first documented that ABCG2 was overexpressed in drug-selective cell lines of ovarian, lung, breast, colon, and gastric cancer [13], and mediates in vitro resistance to a variety of cytotoxic compounds, including mitoxantrone [14], topology Tican, irinotecan active metabolite (SN-38) [15], etc. Moreover, increasing data indicate that individuals with high ABCG2 expression usually respond poorly to chemotherapy [16], which means that tumors expressing sufficient ABCG2 are more likely to develop drug resistance.