ESR1 and breast cancer: In all, 98.3% of these patients were non-responders and as above there was no correlation between EGFR expression and response to gefitinib.23 Similarly, gefitinib as a monotherpay in metastatic estrogen receptor alpha (ER-α) negative BC patients did not provide clinical benefit in another phase II clinical trial.24 Engebraaten et al. tested the efficacy of combining gefitinib with docetaxel in metastatic BC as compared with docetaxel alone.