STAT1 and cancer: STAT1-dependent overexpression of IDO, which blocks T cell activation, has been observed in in several cancers [174] and is linked to high tumor cell PD-L1 in high-grade, triple-negative breast cancer (TNBC), while high U-STAT1 in the TME has been associated macrophage infiltration and poor outcomes in CD68-high patients in two mixed breast cancer subtype cohorts [175].