Background: Tumor-infiltrating lymphocytes (TILs) reflect the antitumor response of the host. This study aimed to assess the value of TILs in predicting pathological response after neoadjuvant chemotherapy (NAC) and survival outcomes in patients with triple-negative breast cancer (TNBC). Methods: A retrospective analysis conducted between February 2012 and December 2015. Patients with stage I, II, and III TNBC patients were enrolled. TILs were assessed in haematoxylin and eosin-stained sections from true cut needle biopsies before NAC. According to international TILs working group, we had three groups; low (0-10%), intermediate (11-59%), and high TILs (≥ 60%). Results: A total of 159 patients was included, 56% were premenopausal and 76.1% were less than 60 years. The main bulk of patients had histological grade III, high Ki 67, and high TILs (74.2%, 84.3%, and 72.3%), respectively. Original Article Predictive and Prognostic Value of Tumor- Infiltrating Lymphocytes for Pathological Response to Neoadjuvant Chemotherapy in Triple Negative Breast Cancer Amrallah A. Mohammed1,2, Fifi Mostafa Elsayed3 Mohammed Algazar4, Hayam E Rashed5 1 Medical Oncology Department, Faculty of Medicine, Zagazig University, Egypt. 2Oncology Center, King Salman Armed Forces Hospital, Tabuk City, Saudi Arabia. 3Department of Clinical Oncology and Nuclear Medicine, Faculty of Medicine, Suez Canal University, Egypt. 4Department of General Surgery, Faculty of Medicine, Zagazig University, Egypt. 5Department of Pathology, Faculty of Medicine, Zagazig University, Egypt. Corresponding Author: Dr. Amrallah A. Mohammed MBBCh, MSc, MD., 29 Saad Zaghloul, Postal code, 44519, Egypt. E-mail: amrallaabdelmoneem@yahoo.com. T; 00201224141040. Fax; +966125532239. The pre-treatment high TILs was significantly correlated with high Ki-67 (p = 0.001), pCR (p <0.001), and late relapse (p <0.001). Other clinico-pathological features such as age, menopausal status, tumor size, histological grade, lymph node involvement and lympho-vascular invasion weren’t significantly correlated with TILs levels. 71.3% of enrolled patients having high TILs achieved pCR, vs 27.8% in the intermediate group and 30.8% in low group. After a median follow-up of 45.3 months, patients with high TILs were significantly associated with longer DFS and OS as compared to intermediate and low TILs (27.2 vs 15.9 vs11.4 months for DFS and 70.2 vs 34.3 vs 27.6 months for OS) p<0.001). Conclusions: Pre-treatment level of TILs had a predictive and prognostic value in TNBC patients receiving NAC. TILs may be integrated into the basic laboratory for TNBC prognostication as a credible biomarker.