AHR and breast cancer: Furthermore, in contrast to previous studies in which AHR expression was downregulated with AHR-specific siRNA in ER+ breast cancer lines [33], no differences were seen in the proliferation rates or viability (>95% by trypan blue and/or propidium iodide exclusion assays) of cells transfected with AHRR or AHR-specific siRNA or in which AHR was deleted by CRISPR-cas9 knockdown (Figure S2).