ERBB2 and breast cancer: When evaluating the signature in different breast cancer subtypes, we observed that high expression of the 19-gene signature, observed in all molecular subtypes (Supplementary Figure S2D), correlated with detrimental RFS (luminal A, HR: 1.56, CI 1.22–1.99; log rank p = 0.00036; luminal B, HR: 1.43, CI 1.06–1.95, log rank p = 0.02; HER2+, HR: 1.71, CI 1.08–2.7, log rank p = 0.02), with more effect in the basal-like subgroup: basal, HR: 2.31, CI 1.65–3.22, log rank p = 4.2 × 10−7 (Figure 4A).