This signature identified ERBB3, which has been previously implicated in lapatanib response.21 To investigate if these cell line-derived signatures were relevant in patient cohorts, we applied our signature to TCGA breast cancer gene expression datasets22 to test the ability to identify patients within the HER2/ERBB2 breast cancer subtype and would likely be sensitive to HER2i. Here, ERBB3 is linked to breast cancer.