Compared with controls, ESR1 A908G mutation-positive cases were significantly more likely to have a first-degree family history of breast cancer (OR = 2.69, 95% CI = 1.15 to 6.28) or a first-degree family history of breast and/or ovarian cancer (OR = 3.48, 95% CI = 1.56 to 7.76), whereas mutation-negative cases did not (OR = 1.22, 95% CI = 0.87 to 1.71 for first-degree family history of breast cancer). This evidence concerns the gene ESR1 and ovarian cancer.