ESR1 and neoplasm: In the validation cohort, there was a significant inverse correlation between SIAH2, ER (P < 0.0001) and PR (P < 0.0001) and a significant positive association with tumor grade (P < 0.0001), patient age (P = 0.009), HER2 (P = 0.007) and intrinsic subtype (P < 0.0001), but not with tumor size or lymph node status (P > 0.05) (Supplementary Table 5 in Additional file 5).