PDCD1 and colonic neoplasm: Next, we further explored the possibility of using CYP19A1 as a target for sensitizing anti-PD-1 therapy, and found that the CYP19A1 inhibitor letrozole sensitized anti-PD-1 therapy in subcutaneous tumors derived from the MC38 and CT26 murine colon cancer (Fig. 10A and B).