we tested the ability of MHC-II expression on tumor cells, to predict immunotherapy-specific benefit in the neoadjuvant breast cancer setting. Quantitative assessment of MHC-II on tumor cells was predictive of durvalumab + NAC and pembrolizumab + NAC...Tumor-specific MHC-II has strong candidacy as a specific biomarker of anti-PD-1/L1 immunotherapy benefit when added to standard NAC in HER2-negative breast cancer.