Emerging evidence suggests that high expression of XBP1s is involved in the oncogenesis, progression, and development of therapeutic resistance in breast cancer.[12, 17, 33] Particularly, transcriptomic analysis and clinical‐based studies have revealed that elevated expression of XBP1 is an important gene expression signature in estrogen‐positive breast cancer.[34] In concordance, our data showed high expression of both XBP1 and XBP1s specifically in HR+/HER2− breast cancer. The gene discussed is XBP1; the disease is breast cancer.