Background: Monoclonal antibodies against PD-1 or PD-L1 are established in clinical practice for the treatment of both early and advanced/metastatic triple-negative breast cancer. Beyond the established immune checkpoints (ICPs) (PD-1 and CTLA-4) additional ICPs such as lymphocyte activation gene-3 (LAG-3) are subject of current research. In the present retrospective gene ex-pression analysis, we evaluated the prognostic significance of LAG-3 in 461 patients with early breast cancer. In addition, we examined whether there was a correlation between the different ICPs and CD8 expression. Methods: Using microarray-based gene expression analysis, we examined the prognostic signif-icance for metastasis-free survival (MFS) of LAG-3 mRNA expression in the whole cohort of 461 breast cancer patients and among different molecular subtypes. Correlations were analyzed us-ing Spearman-Rho correlation coefficient. Results: In the whole cohort, LAG-3 expression had no significant impact on MFS (p = 0.712, Log Rank). In the subgroup analyses, there was a trend, that higher LAG-3 expression was associated with favorable outcome in the luminal B (p = 0.217), basal-like (p = 0.370) and HER2 (p = 0.089) subtypes, although significance was not reached. In contrast, in multivariate Cox regression analysis adjusted for age, tumor size, axillary nodal status, histological grade of differentiation and the proliferation marker Ki-67, LAG-3 showed a significant influence on MFS (HR 0.574; 95% CI 0.369–0.894; p = 0.014). High LAG-3 significantly correlated with CD8 ( = 0.571; p < 0.001). Conclusion: LAG-3 expression had an independent impact on MFS. In addition to PD-1 and PD-L1, further immune checkpoints such as LAG-3 could serve as therapeutic targets in breast cancer.