GPER1 and breast cancer: These signalling pathways play an important role in the proliferation, metastasis and formation of drug resistance of human tumours.22, 23 G1 (GPR30 agonist) and G15 (GPR30 inhibitor) are quinoline derivatives that are widely used to activate or block GPR30 signalling and are used to explore the potential of GPR30 as a therapeutic target.24, 25 A recent study showed that targeting GPR30 reduced metastasis and drug resistance in breast cancer.26 However, few studies have investigated the effect of targeting GPR30 in gastric cancer.