To discover new regulatory pathways in B lymphoma cells, we performed a combined analysis of experimental, clinical and global gene expression data. We identified a specific cluster of genes that was coherently expressed in primary lymphoma samples and suppressed by activation of the B cell receptor (BCR) through aIgM treatment of lymphoma cells in vitro. This gene cluster, which we called BCR. 1, includes numerous cell cycle regulators. A reduced expression of BCR. 1 genes after BCR activation was observed in different cell lines and also in CD10(+) germinal center B cells. We found that BCR activation led to a delayed entry to and progression of mitosis and defects in metaphase. Cytogenetic changes were detected upon long-term aIgM treatment. Furthermore, an inverse correlation of BCR. 1 genes with c-Myc co-regulated genes in distinct groups of lymphoma patients was observed. Finally, we showed that the BCR. 1 index discriminates activated B cell-like and germinal centre B cell-like diffuse large B cell lymphoma supporting the functional relevance of this new regulatory circuit and the power of guided clustering for biomarker discovery.