ESR1 and breast cancer: In order to study the possible implication of AHR expression on the expression of genes involved in the AHR signaling pathway regardless of ERα status, mRNA levels of 54 candidate genes were therefore analyzed in the two subpopulations (ERα-positive and ERα-negative) of this cohort of 439 breast cancers: 26 low AHR-expressing and 26 high AHR-expressing ERα-negative breast tumors, and 14 low AHR-expressing and 14 high AHR-expressing ERα-positive breast tumors.