ABCG2 and neoplasm: Several studies in cells and mice have validated that, in addition to tumor-supportive functions, GH specifically promotes chemoresistance in tumor cells via upregulation of specific multidrug efflux pumps called ABC transporters which function to actively remove a wide range of chemotherapy drugs from tumor cells; upregulation of molecular markers of metastasis (EMT markers); and inhibition of apoptosis [8,10,11,37].