Background: Current evidence makes reference to the potential role that tumor-infiltrating lymphocytes (TILs) as a prognostic factor in breast cancer and numerous types of tumors. Different studies have shown that the interaction with the immune response of the host is relevant to the response to chemotherapy. TILs are cell phenotype T CD3 +, which can, in turn, stratify in cytotoxic T lymphocytes (CD8), and regulatory T cells (CD4+ CD25+ FOXP3+).Our aim was to identify whether there was a relationship between TILs and SLE in patients with stage I to III breast cancer who have undergone chemotherapy adjuvant treatment. The secondary endpoint was to analyze the association between subtype infiltrating lymphocytes (CD4 and CD8) and SLE. Methods: Retrospective and analytical study in our institution IONC. Patients with stage I to III breast cancer was analized which had standard risk factors and required adjuvant treatment with chemotherapy. 87 patients completed with the selection criteria. The infiltration degree by H/E was evaluated and CD4 and CD8 by IHQ was marked. SLE was analyzed through the Kaplan-Meier method. Results: 87 samples were analyzed, in 46 patients (52,8 %) evidenced TILs and in 41 patients (47.12%) there were no TILs in their tumor samples. SLE was higher for those patients who had TILs with respect to those patients who did not have any TILs, 45.3 months as opposed to 30.85 months respectively (p: 0,038) and these differences were statistically different. In the TILi analysis, it could observed that 91% patients not revealed infiltrations in their tumor samples.When correlating CD4 and CD8 was carried out, 33% of the patients showed CD4 TILs in their tumor samples and 49.4% evidenced CD8 TILs. There were no SLE differences regarding the presence or the absence of CD4. The high number of CD8 was associated to a higher SLE; 39.06 months as opposed to 37.5 months, but these differences were not statistically different. Conclusions: We could conclude that patients who had showed TILs in their tumor samples had a higher SLE with respect to those who did not show any infiltration and this was statistically significant. There were no differences when samples were analyzed on the presence or absence of CD4 and CD8.