Estrogen receptor-negative (ER−) cells were used since there remains an unmet medical need for targeted therapeutics for ER- breast cancers and since interpretation of outcomes involving the AHR in ER+ cells is confounded by the well-established cross-talk between the AHR and ER signaling pathways [47,48,49,50,51,52]. This evidence concerns the gene ESR1 and breast carcinoma.