ERBB2 and breast cancer: Inflammatory breast cancer (IBC) is rare, constituting only 1–5% of breast cancers, yet contributes to approximately 10% of breast cancer-related mortality in the United States.1,2 Treatment for IBC has improved over recent decades with increasingly effective systemic therapy, particularly with regards to targeted therapies (e.g., trastuzumab, pertuzumab) for HER2-positive (HER2+) disease.3-5