ESR1 and breast cancer: Conversely, in another retrospective study of 105 women with advanced breast cancer treated with fulvestrant during any line of therapy, patients who are overweight and obese had almost a 2.5-fold decreased clinical benefit rate (defined as the proportion of partial or complete responses or stable disease lasting at least 6 months) when treated with fulvestrant compared to patients with normal weight (p < 0.001) irrespective of the estrogen receptor expression [60].