Gene Expression Differences between Low and High Stage Diffuse Large B Cell Lymphoma (DLBCL).

Low stage DLBCL patients have better prognosis than those with advanced disease. We searched for differences in gene expression between disease stages to find correlations with tumor stage as possible therapeutic targets. We used 2 microarray datasets from the Leukemia/Lymphoma Molecular Profiling Project containing nodal and extra-nodal de novo DLBCL samples on Lymphochip (LC), spotted arrays of ~7400 and Affymetrix arrays (Affy) of ~45,000 elements. The Affy dataset was a subset of the LC samples. LC elements were median-centered, log₂ transformed; Affy elements were array-centered to a 500 average. We compared average gene expression in stage I vs. III/IV, looking for elements with >2-fold differences between low and high stage, with p<.05, excluding Affy elements with an average <100. 35 stage I and 131 stage III/IV samples were analyzed with LC and 34 stage I and 118 stage III/IV samples with Affy. Differentially expressed genes were searched by NCBI Entrez and Stratagene PathwayArchitect software to find common pathways of regulation. From the LC data, 6 genes were identified as differentially expressed, 5 were higher in stage I, 1 was lower in stage I. For the Affy data, 29 genes were differentially expressed, 11 were higher in stage I, 18 were lower in stage I (Table 1). Differences were rarely >3-fold. A subset of these genes, CTGF (connective tissue growth factor), FN1 (fibronectin), INHBA (activin), POSTN (periostin), THBS1 (thrombospondin), and BCL2, are coregulated and/or coregulatory. Many are expressed in the microenvironment and associated with fibrosis, wound healing and Th2 immune response. The presence of these genes at higher levels and their known associations implied a pathway of TGF-β signaling present mainly in the low stage DLBCL. Although TGF-β levels were not different between stages, differences in localization/activation of TGF-β could account for observed differences. In conclusion, there are a small number of stage-specific gene expression differences in DLBCL, and many of these relate to TGF-β signaling in the microenvironment. CTGF and FN1 were previously identified as key prognostic molecules in DLBCL (Rosenwald et al, NEJM 2002). These differences may relate to different prognoses between DLBCL stages and constitute therapeutic targets.