The results showed that HR+/HER2− breast cancer samples with high CEACAM6 expression had significantly elevated predicted IC50 values for several commonly used chemotherapeutic agents, including cyclophosphamide, epirubicin, paclitaxel, and 5-fluorouracil, as well as for endocrine therapies such as tamoxifen and fulvestrant. Here, CEACAM6 is linked to breast cancer.