IDO1 and breast cancer: We have recently shown that exercise can counteract radiation-associated increase in Kynurenine levels and IDO/TDO activity in breast cancer patients as well as reduce IDO (serum Kynurenine/Tryptophan Ratio) and Kynurenine levels significantly in pancreatic cancer patients (Zimmer et al. 2019; Pal et al. 2021).