Introduction: Immune system plays an important role in behavior of cancer. Breast cancer and its stroma display high levels of immune-cell infiltrates (tumor-infiltrating lymphocytes TILs). Programmed cell death-ligand 1 (PD-L1) is one key inhibitor mechanism for TILs. Potential of TILs and PD-L1 as predictive factors for chemotherapy response in breast cancer is a promising field of study. The aim of this work is to investigate the correlation of PD-L1, TILs and pathologic response following neoadjuvant chemotherapy (NAC) in breast cancer patients and effect of NAC on PD-L1 expression and TILs in residual tumor mass. Methods: Thirty patients with invasive duct carcinoma diagnosed by core biopsy and received NAC were enrolled in this prospective study from November 2018 to October 2020. PD-L1 expression was evaluated by immunohistochemistry and relates this to TILs, clinical characteristics, and response to neoadjuvant chemotherapy and then re-evaluated in residual masses after surgery. Results: PD-L1 expression was observed in 40% of cases in the tumor cells. High stromal TILs were detected in 46.7%. Also, 64.3% and 58.3% of patients expressed TILs and PD-L1 (respectively) in their core biopsies gained complete clinical and pathologic responses with significant difference (p value < 0.001; 0.013). High PD-L1 expression and high TILs were observed in triple negative breast cancer (TNBC) and Her2 enriched cases but without significant difference. Conclusion: High TILs and PD-L1 are associated with complete clinical and pathologic responses in breast cancer patients who receiving NAC. © 2021 SESPM. Published by Elsevier Espana, ˜ S.L.U. All rights reserved