The analysis of a bulk RNA-seq data set with a mixed cohort of melanoma and non-melanoma skin cancer patients revealed a significant positive correlation of IDO1 with GLI2 (R = 0.39, p < 0.01), supporting an in vivo involvement of the HH/GLI pathway in the induction of IDO1 (Fig. 6A). Here, IDO1 is linked to skin neoplasm.