ESR1 and metastatic neoplasm: Similarly, mutation frequencies in the ER gene (ESR1) differ between primary and metastatic tumors, as seen through large-scale next-generation sequencing of postmenopausal women with ER + metastatic breast cancer treated with everolimus in combination with exemestane within the BOLERO-2 trial, as presented by Dr Piccart at the 2013 IMPAKT meeting (unpublished observations, Martine Piccart).