ERBB2 and breast cancer: Expression of ER, PR, HER2 are the most recognized indicators.23 Since bias in molecular typing among BC samples might have unknown confounding effects, we specially constructed three pooled samples (1 HER2+HR‐, 1 HER2‐HR+, 1 HER2‐HR‐) with only one random sample rather than obtain plasma pool samples completed by random choice.