ESR1 and neoplasm: In the primary cohort, there was a significant inverse correlation between SIAH2 protein expression and ER (P < 0.0001), PR (P = 0.011) and a positive association with tumor grade (P < 0.0001) and intrinsic subtype (P = 0.028), but there was no association with patient age, tumor size, lymph node status or HER2 (all P > 0.05) (Supplementary Table 4 in Additional file 4).