HLA-DR level in cytotoxic T cells is a clinically validated predictive biomarker of breast cancer patients’ response to NACT. (A) Percentage of infiltrating cytotoxic T cells (CTLs) in NACT-responders (black dots, 1st cohort n = 13 and 2nd cohort n = 11) and non-responders (red dots, 1st cohort n = 17 and 2nd cohort n = 20) breast cancer patients. (B) HLA-DR expression level in CTLs in the same patients as in (A). (C) ROC curve analysis of HLA-DR level in CTLs for the 1st cohort (black lines), 2nd cohort (grey lines), and merged cohorts (blue lines). (D) Forest plot of the multivariate analysis performed with both cohorts, including the odds ratio (with 95% confidence interval) and the p-values. (E) Predictive probability model of response to NACT according to the HLA-DR level in CTLs (merged cohorts). * p < 0.05, ****p < 0.0001.