The elevated concentration of serum kynurenine in B[a]P exposed mice on a HFD may be more reflective of the amount of total body AhR activation and/or tumor AhR activation, as the transcriptional activity of AhR induces indoleamine 2,3-dioxigenase (IDO), the enzyme responsible for the catabolizing tryptophan to kynurenine. Here, IDO1 is linked to neoplasm.