Tumors that gave first rise to bone metastases were frequently ER positive and/or PgR positive (67.6%) and rarely EGFR-positive (15.7%), whereas breast cancers that gave first rise to lung metastases often expressed HER2 (48.5%) and EGFR (45.5%), very frequently expressed either HER2 or EGFR (75.8%), and infrequently expressed PgR (27.3%). This evidence concerns the gene ESR1 and breast cancer.