As RA increased the PD‐L1 surface expression on tumor cells (Figure S8A,B, Supporting Information), and increased PD‐L1 abundance in tumors improves the efficacy of anti‐PD‐1 immunotherapy,[33, 34] we therefore investigated whether combination treatments of RA and anti‐PD‐1 have synergistic anti‐tumor effects in the MC38 tumor model. The gene discussed is CD274; the disease is neoplasm.