ESR1 and breast cancer: Recently, it was reported within the I-SPY 2 trial that ER+/80-GS Basal-type tumors have higher expression of basal-type keratins (keratins 5/14/17) compared with ER+/Luminal-type tumors.20 This supports the finding of Cheang et al. who identified EGFR and cytokeratin 5/6 expression by immunohistochemistry as prognostic markers for basal-like breast cancers.21