Frequency of BCL-2 rearrangement, t(14; 18), in Thai patients with follicular lymphoma

Abstract

Follicular lymphoma is characterized by the specific chromosomal translocation t(14;18). This translocation involves the immunoglobulin heavy chain (IgH) gene on chromosome 14 and the B-cell lymphoma-2 (BCL-2) gene on chromosome 18, resulting in dysregulated expression of the anti-apoptotic BCL-2 gene in lymphoma cells. The incidence of follicular lymphoma in Asian population is much lower than that of Western countries suggesting the differences in pathogenesis. In this study, we analyzed t(14;18) translocation in 40 paraffin-embedded tissues from Thai patients with follicular lymphoma using polymerase chain reaction (PCR) and fluorescence in situ hybridization (FISH) assays. Three primer pairs for major breakpoint region (MBR), minor cluster region (mcr) and intermediate cluster region (ICR) were used. The t(14;18) translocation was found in 6 of 40 cases (15%) by PCR; 5 (12.5%) had translocation at the MBR breakpoint and 1 (2.5%) at the ICR breakpoint, whereas translocation in mcr breakpoint was not found. Eight cases were analyzed by FISH. Three cases were successfully probed, and two of them showed positive translocation signal. One of the these two was negative for t(14;18) translocation by PCR. The results indicate that frequency of t(14;18) translocation in Thai patients with follicular lymphoma is much lower than in Western patients. Two possible explanations are 1.) BCL-2 translocation is not absolutely required for lymphomagenesis in Thais and/or 2.) the translocation is present but at different breakpoints undetectable by PCR.