Therefore, this study examines and compares the clinical outcome of resectable HER2-low (IHC1+ or IHC2+/ISH-Negative) and HER2-zero (IHC 0) breast cancer and its prognostic association with the Oncotype Dx RS in HR+ breast cancer using the NCDB, a US national cancer outcome database. The gene discussed is ERBB2; the disease is cancer.