PGP and gastric cancer: Currently, a series of miRNAs, such as miR-103/107, miR-459, miR-361, miR-21, miR-19a/b and mir-129, have been shown to regulate the resistance of GC cells to chemotherapeutic drugs by directly or indirectly targeting P-gp (55, 57, 98, 105, 136, 137).