Even though, as mentioned above, the up-expression IDO1 has been described in various human tumor tissues not only in tumor cells but also in other components of the TME, and the IDO1 expression status in patients has also been explored in some clinical trials to assess its relevance with poor prognosis (126), not all tumor progression or poor prognosis has a positive correlation with high IDO1 expression (127, 128). Here, IDO1 is linked to neoplasm.