GEO data (GSE35261, GSE30784, GSE26549, and GSE85195 combination), including 56 normal tissues, 78 OLKs, and 212 OSCCs, revealed a higher expression of IDO1 in OLK and OSCC than in para-cancer tissue (Figure 6C) and a positive relationship between IDO1 and CD68 expression in OLK (Figure S5B). Here, IDO1 is linked to cancer.