IDO1 and neoplasm: Theate et al. assessed IDO1 expression by immunohistochemistry on tissue microarrays in 15 common solid tumor types with about 17–60 samples of each and found that the IDO1 expression could be identified in total 383 of 624 samples (61 %), but was limited to a small fraction of cells, and the proportion of IDO1-expressing cells widely varies according to the tumor type[101].