The aim of the project was to identify biological variables in high-clinical-risk patients with diffuse large B-cell lymphoma (DLBCL), treated with risk-adapted therapies. The study was performed in a series of high-clinical-risk patients with DLBCL treated with MegaCHOP or MegaCHOP + IFE followed by autologous stem-cell transplantation (ASCT). An initial reduced set of diagnostic tumoral samples was studied by gene expression profiling and gene-set-enrichment analysis. A set of potential biomarkers extracted from this study was then explored in tissue microarrays containing paraffin-diagnostic tissue from 50 patients. The statistical analysis identified 17 immunohistochemical markers associated with the clinical endpoints. A subsequent multivariate analysis identified FoxP3+ T-reg cells as an independent predictor of failure-free survival. Bcl6 expression, CG/ABC subclasses and IPI were found not to predict survival in this series. The increased presence of regulatory T-cells as a marker of adverse outcome highlights specific components of the tumoral microenvironment in the pathogenesis and treatment response prediction for high-clinical-risk patients with DLBCL.