GPER1 and malignant colon neoplasm: We discovered that CYP19A1 inhibition by letrozole or si-CYP19A1 downregulated GPR30, p-Akt and PD-L1 in HCT116 and HT29 colon cancer cells (Fig. 8A), which were greatly enhanced by exogenous addition of estradiol (Fig. 8B).