ERBB2 and breast cancer: These recommendations were, however, designed with the aim of allocating HER2-positive patients to HER2-targeted treatment with trastuzumab, and while the distinction between positive and negative cases has shown good inter-observer reproducibility [9–13], reasonable consistency among laboratories [14–16], and high concordance between biopsy and surgical specimen [17–19], the discrimination of HER2-low BC may not show similar robustness.