ESR1 and cancer: In the California Teachers Study (CTS), which has actively followed female California public school professionals for incidence of cancer and other outcomes since 1995, we previously reported that increased strenuous recreational physical activity, but not moderate intensity recreational physical activity, was associated with reduced risk of invasive breast cancer; moreover, the association was confined to ER-negative (ER–) as well as ER–/PR– invasive breast cancer in the analyses for ER-defined or ER/PR-defined subtypes [3].