Among 54 women with estrogen receptor (ER)-positive advanced BC progressing after endocrine treatment and chemotherapy, 17 women (31.5%) experienced a radiological response (95% CI 19.5 to 45.6, 17 partial responses), with a median duration of response of 8.7 months (95% CI 3.7 to 12.7) and a median PFS of 5.5 months (95% CI 3.6 to 7.6) and a median OS of 12 months (95% CI 9.0 to 18.2). This evidence concerns the gene ESR1 and breast cancer.