Since our study found that elevated IDO1 is associated with a better prognosis for breast and ovarian cancer, there have been several reports correlating IDO1 expression with poor patient prognosis, including those diagnosed with colorectal cancer,20 prostate cancer,21 acute myeloid leukaemia,22 glioblastoma,23 non‐small‐cell lung cancer24 and oesophageal cancer.25 Here, IDO1 is linked to colorectal cancer.