Background & Objective: Tumor-infiltrating lymphocytes (TILs) develop as recognition and defense against malignant cells by the host immune system. T cells are the most tumor infiltrating immune cells. There are controversial data about intratumor T cells and many have proposed diverse mechanisms for dysfunction of TILs. The aim of this study is analyzing Tumor Infiltrating T lymphocytes in patients with breast cancer by immunophenotyping.

 Methods: Sixteen women suffering from breast cancer were examined thirteen of them were confirmed histologically to be invasive ductal carcinoma (IDC). Tissue samples from patients and matched control group were processed for analysis by flow cytometry.

 Results: Results indicated that human breast cancer contain variable numbers of TILs. No significant changes in the percent of intratumor CD45⁺, CD3⁺ and CD3⁺/CD45⁺ cells were observed between studied group. Also there were no significant differences between cancer patients (group 1 and 2) and control group in the case of infiltration and activation status of T cells subpopulations. CD4⁺ cells in IDC patients and CD8⁺ cells in patients with other tumors (ILC+AMC) were the most infiltrated TILs. Intratumor TCD8⁺ cells expressed HLA-DR markers significantly more than CD25 as activation marker. In this investigation we could not find any correlation between TIL and both size and clinical stages of tumor.

 Conclusion: An immune infiltrate is an invariable finding in breast cancers, with considering the activation marker expression, TIL may be activated, albeit partially. Understanding the insensitive and/or suppressive nature of cancer cells to the immune system may provide important insights into tumor escape mechanisms as well as the development of anti-cancer strategies.