PD-L1 expression was explored by immunohistochemistry in breast cancer tissue sections, providing evidence that: (i) PD-L1 is expressed in 20–40% of breast cancers; (ii) PD-L1 expression is significantly higher in invasive breast cancer tissue than in normal mammary tissue; (iii) among the various breast cancer subtypes, TNBC clearly expresses PD-L1 more frequently than other subtypes; and, (iv) in TNBCs, PD-L1 tumor expression is positively associated with stromal TIL levels [538]. The gene discussed is CD274; the disease is breast cancer.