CD274 and breast cancer: Interestingly, the variation in PD-L1 expression between TNBC and HR+/HER2- breast cancer was also evident in screening participants for the KEYNOTE-012 TNBC study, in which 59% of the total screened had PD-L1+ tumors (141) compared to the KEYNOTE-028 HR+/HER2- study, where only 19% of the total screened were PD-L1+ (140).