ESR1 and breast cancer: Association between SSRI prescription and breast cancer recurrence within strata of (a) Group I, women with tumors that expressed the estrogen receptor and who received at least one year of tamoxifen therapy (ERP+/TAM+), or (b) Group II, women with tumors that did not express the estrogen receptor, and who never received tamoxifen therapy, and who survived at least one year after diagnosis (ERP−/TAM−).