LAUSR

Key Points Question Do the demographics, clinicopathologic characteristics, and prognosis differ between breast cancers with no erb-b2 receptor tyrosine kinase 2 (ERBB2; formerly HER2 or HER2/neu) expression (ERBB2 negative) and those with low-level ERBB2 expression (ERBB2 low)? Findings In this cohort study of 1 136 016 patients from the National Cancer Database in the US, the proportions of ERBB2-low breast cancer were slightly lower among Hispanic and non-Hispanic Black patients compared with non-Hispanic White patients. ERBB2-low status was associated with slightly improved overall survival (≤2% difference at 5 years) compared with ERBB2-negative cancer. Meaning The findings of this study suggest that treatment response and long-term outcomes may be similar in ERBB2-low and ERBB2-negative cancers and do not support the classification of ERBB2-low breast cancer as a unique disease entity.