CD274 and breast cancer: Using a common definition of TMB-high as ≥ 10 mut/MB, approximately 5% of all breast cancer cases (including all breast cancer subtypes) are considered TMB-high, compared to 4% TIL-predominant (defined by ≥ 50% lymphocyte infiltration) and 10% PD-L1-positive (defined by ≥ 1% tumor or immune cell expression) [7, 15, 17, 18].