ESR1 and breast carcinoma: Likewise, in the setting of postmenopausal nonsteroidal aromatase inhibitor-resistant ER + HER2- breast cancer patients treated with everolimus and exemestane, comprehensive sequencing analysis did not identify predictive biomarkers, although patients with PIK3CA exon 9 mutations experienced a quantitative benefit compared to patients with PIK3CA exon 20 mutations [380].