Consistent with a favorable benefit of immunotherapy in HER2+ BC patients with PD-L1-positive tumors in clinical trials 45, 46, HER2+ BC in low IRPI group tended to have high expression level of ICMs such as PD-L1, CTLA4, IDO1, HAVCR2 and LAG3, illustrating the feasibility and power of our index. This evidence concerns the gene IDO1 and breast cancer.