A Study On The BCL-6 Gene Alterations In B-cell Non-Hodgkin's Lymphomas In Chinese Populations

Objective: To investigate the BCL-6 gene alterations in B-cell Non-Hodgkin's lymphomas( B-NHL) in Chinese populations and its clinic-pathological significance.Methods:Morphologic studies and immunohistochemical analyses of BCL-6, CD10 and BCL-2 protein expression were performed on 135 cases of B-NHL frequently occurred in Chinese populations and 5 cases of T-NHL, 5 cases of nodular lymphocyte predominance Hodgkin's lymphoma (NLPHL) and 10 cases of reactive hyperplasia of lymph node (LRH) with paraffin-embedded tissues. Polymerase chain reaction (PCR) and direct DNA sequencing method were used to identify mutations in the 5'-noncoding region of the BCL-6 gene in all above metioned samples. House-keeping gene β-Actin was used to detect the quality of DNA. Using interphase fluorescence in situ hybridization (FISH) with dual color breakapart probe to identify rearrangements of the BCL-6 gene in 22 cases of nodal diffuse large B-cell lymphoma (DLBCL) paraffin-embedded tissues and 10 cases of nodal DLBCL fresh tissuses as well as 5 cases of LRH paraffin-embedded tissues.Results: (1) BCL-6 and CD10 protein were expressed almost exclusively in LRH, nodal DLBCL, extranodal DLBCL, follicular lymphoma (FL) and Burkitt's lymphoma (BL), the rates of positivity were 100%(10/10)and 100%(10/10),72.7%(16/22)and 40.9%(9/22),75.9%(22/29)and 41.4%(12/29),88.9%(16/18)and 72.2%(13/18)as well as 100%(5/5)and 100%(5/5), respectively. BCL-6 and CD10 protein were not expressed in other B-NHL such as small lymphocytic lymphoma (B-SLL), mantle cell lymphoma (MCL), extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT-L), Lymphoplasmacytic lymphoma(LPL) and lymphoblastic lymphoma (LBL) as well as T-NHL and NLPHL. BCL-2 protein were expressed in nodal DLBCL, extranodal DLBCL, FL, B-SLL, MCL, MALT-L and LBL, the rates of positivity were 36.4%(8/22), 27.6%(8/29), 83.3%(15/18), 88.9%(16/18), 86.7%(13/15), 72.7%(13/18)and 33.3%(1/3), respectively. BCL-2 protein were not expressed in LPL, BL, T-NHL and NLPHL. (2) BCL-6 protein expression in DLBCL could be classified into four patterns: GC/FL pattern, intermediate pattern, sporadic pattern and rare or absent pattern. The coexpression of BCL-6 and CD10 was observed in 40.9%(9/22) nodal DLBCL, 41.4%(12/29) extranodal DLBCL, 72.2%(13/18) FL and 100%(5/5) BL. Among them the BCL-6 protein expressions were GC/FL pattern. Low clinic stage (stageⅠandⅡ) was more frequent in cases with coexpression of BCL-6 and CD10 than those without(p<0.05) . (3) the incidence of BCL-6 mutations in 135 cases of B-NHL was 14.8%(20/135), among them 6 cases of nodal DLBCL(27.3%),4 cases of FL(22.2%),4 cases of MALT lymphoma(22.2%) ,4 cases of extranodal DLBCL(20.7%)and 1 cases of LRH(10%) were found to have mutions. There are no significantly differences of incidences of BCL-6 gene mutations between nodal and extranodal DLBCL (p>0.05). Mutations are absent in T-NHL and NLPHL(P<0.05). All mutations are base substitutions and the frequency of single-base changes were 0.14×10-2 /bp~0.68×10-2 /bp. No association between BCL-6 mutation and clinical characteristics was found except that BCL-6 mutated patients had a signicantly higher LDH level (p<0.05). (4)the incidence of BCL-6 gene rearrangement in nadal DLBCL was 28.1%(9/32), among them those in paraffin-embedded DLBCL was 27.3%(6/22) and those in fresh DLBCL was 30%(3/10), no significant difference was found between them(p>0.05) . BCL-6 gene rearrangement was not found in all five cases of LRH, there is significant difference between LRH and DLBCL(p<0.05) . No association among BCL-6 gene rearrangement, protein expression and mutation was found(p>0.05).Conclusions:(1) BCL-6 and CD10 protein were expressed mainly in DLBCL, FL and BL of B-NHL in Chinese population. Detection of BCL-6 and CD10 protein expression in combination may contribute to the diagnosis of DLBCL, FL and BL, especially to DLBCL which arises from GC-B cell. (2) BCL-6 protein expression in DLBCL could be classified into four patterns: GC/FL pattern, intermedia...