Human epidermal growth factor receptor 2 (HER2) status in breast cancer: practice points and challenges

Human epidermal growth factor receptor 2 (HER2)‐enriched breast cancer benefits significantly from anti‐HER2 targeted therapies. This highlights the critical need for precise HER2 immunohistochemistry (IHC) interpretation serving as a triage tool for selecting patients for anti‐HER2 regimens. Recently, the emerging eligibility of patients with HER2‐low breast cancers for a novel HER2‐targeted antibody–drug conjugate (T‐DXd) adds challenges to HER2 IHC scoring interpretation, notably in the 0–1+ range, which shows high interobserver and interlaboratory staining platform variability. In this review, we navigate evolving challenges and suggest practical recommendations for HER2 IHC interpretation.