Clinical, epidemiologic, and pathologic significancer of HER2-low expression in breast cancer

It is unclear whether breast cancer (BC) with low HER2-expression (IHC 1+ or 2+) is a distinct clinical, pathological, and epidemiological entity from BC classified as HER2-negative. In a cohort study of 2200 patients with HER2-low or HER2-negative BC, there were differences in hormone-receptor status, family history, and self-identified race and ethnicity between HER2-low and HER2-negative status. Within hormone receptor-negative tumors, HER2-low status was associated with better survival outcomes compared with HER2-negative status. The authors conclude that these findings suggest that HER2-low BC might be a distinct biologic entity.