IDO1 and breast cancer: Importantly, the AhR has been demonstrated to regulate the expression of immune-regulatory markers including Arg1, IDO, IL-10, COX-2, C/EBPβ, and S100A9 (Vogel et al., 2008; Bankoti et al., 2010; Benson and Shepherd 2011; Simones and Shepherd 2011; Vogel et al., 2013; Neamah et al., 2019; Dahlem et al., 2020), which are critical factors in the pathogenesis of breast cancer (Yu et al., 2013; Yu et al., 2014; Dey et al., 2021).