Key genes have been identified, including oncogenes encoding hormone receptors (ER and PR) and tyrosine kinase receptors (ERBB2, EGFR), and tumor suppressor genes (TSG) such as TP53, BRCA1, and BRCA2. However, our molecular understandings of breast cancer, together with clinical benefits for patients, remain limited. This evidence concerns the gene BRCA1 and breast cancer.