Consistent with this observation, previous studies have shown that tumors with 1%–9% ER positivity closely resemble TNBC: Fujii et al. reported minimal benefit from adjuvant ET in this subgroup,11 and Iwamoto et al. demonstrated that most tumors with 1%–9% ER expression were molecularly similar to ER-negative, basal-like cancers.9 Here, ESR1 is linked to cancer.