Prognostic Significance of Promoter Methylation of Multiple Genes in Germinal Center Hyperplasia (GCH) and Lymphomas of Germinal Center Origin.

Germinal centers (GC) are unique sites in peripheral lymphoid tissue where clonal selection of B cells takes place. GC have been known to be a major source of B-cell lymphomas, including follicular (FL) and diffuse large cell (DLCL). DNA methylation of tumor-suppressor genes is a mechanism of gene silencing involved in the pathogenesis of FL and DLCBLs. Much less is known about the role of methylation in GCH. We determined the methylation status of 5 tumor-suppressor genes in 50 patients with lymphoma of GC origin and 50 GCH in order to find any differences between the pathological and the physiological state as well as its prognostic significance. MATERIAL AND METHODS. Genomic DNA extracted from paraffin-embedded samples of 30 DLCL, 20 FL and 50 GCH were analyzed by methylation-specific polymerase chain-reaction to determine promoter hypermethylation of DAP-k, SHP1, Rarβ, p14 and MGMT. Methylation status of each gene was correlated with clinicopathological status. Overall survival (OS) rates were calculated by the Kaplan-Meier method and differences were compared with the log-rank test. RESULTS. Median age was 65 in patients with lymphoma and 19 for GCH. Sex distribution was similar in all entities (60% females). Both lymphoma groups were balanced with respect to the presence of B symptoms, bulky disease, bone marrow infiltration, advanced stage and high IPI/FLIPI. DAP-k promoter methylation was present in more patients with lymphoma (89 and 87%) than with BFH (37%) p<0.0001. RaRB was methylated with higher frequency in FL (60%) than in DLCL (23%) and FH (12%) p<0.0001. SHP1 was more frequently methylated in FL (67%) and GCH (58%) than in DLCL (20%) p=0.01. Promoter hypermethylation of SHP1 was significantly associated with longer OS (p=0.021). Methylation of RaRB, p14 and MGMT were associated with shortened OS but the differences were not statistically significant. Those patients with DAPK methylated live longer but not significantly. In multivariate analysis hypermethylation of none of the genes studied remained an independent prognostic factor. CONCLUSIONS. Inactivation of DAP-K, and Rarβ is present in GC lymphomas with significantly higher frequency than in BFH. Thus, it may have pathogenic significance. SHP1 is methylated more frequently if FL and BFH than in DLCL, therefore that gene may be associated with aggressive disease. Methylation of DAP-k, SHP1, Rarβ, p14 and MGMT has no significant impact on overall survival. Markers for aberrant methylation may represent a promising way to monitor the onset and progression of malignancies but more extensive and prospective trials are needed to precisely define its role.

No relevant conflicts of interest to declare.