Phase I–II clinical studies with small sample size, such as GIADA (NCT04659551) (4), KEYNOTE-028 (NCT02054806) (5), NCT02779751 (6), NCT03051659 (7), and more (8), provided the preliminary efficacy and safety data of ICIs in HR+/HER2– breast cancer. This evidence concerns the gene ERBB2 and breast cancer.