ESR1 and breast cancer: We confirmed the association between CHK2 dysregulation and poor outcome for patients with ER+/HER2− breast cancer using proteomic data for phosphor-CHK2 (TCGA: HR = 2.0, P = 0.02) (Fig. 8B) and validated the observed enrichment for CHK2 dysregulation in ER+/HER2− disease relative to either HER2+ (1.5-fold) or TNBC (10-fold) at the protein level (P = 0.0004; Fig. 8C).