Overall we found that SASH1 was associated with favourable prognosis, but stratifying the cases based on ER status revealed that this was driven by the more prevalent ER-positive cases (75–80% of the cohorts analysed), and SASH1 expression was inversely associated with outcome in ER-negative, TNBL and HER2+ breast cancers. This evidence concerns the gene ESR1 and breast cancer.