Conversely, trastuzumab has no effect on cell lines and xenografts with low HER2 expression.38 However, the recent results of the NSABP B-47 trial undermine this theory by showing that adjuvant trastuzumab in patients with HER2 1+ or 2+ breast cancers by IHC does not improve disease- or relapse-free survival in this population.16 One possible explanation is that moderate HER2 expression is challenging to detect by IHC because of its semi-quantitative nature and its narrow dynamic range. The gene discussed is ERBB2; the disease is breast carcinoma.