Distinct Distributions Of Immunohistochemical Subgroups, Cytogenetic Profiles And BCL2 Expression Mechanism Of Diffuse Large B-cell Lymphoma In Chinese Patients

Objective:(1) To study the distributions of germinal center B-cell-like(GCB) subgroup and non-GCB subgroup of diffuse large B cell lymphoma(DLBCL) in Chinese patients.(2) To investigate the cytogenetic alterations of DLBCL and its subgroups in Chinese patients.(3) To explore the possible mechanisms of BCL2 expression in DLBCL and its subgroups in Chinese patients.Methods:(1) Immunohistochemical analysis for CD10,BCL6,MUM1,GCET1 and FOXP1 was performed on 124 cases of de novo DLBCL from Shanghai hospitals. Hans algorithm and Choi algorithm were applied to classify DLBCL into GCB and non-GCB subtypes.To be a comparative study,114 cases of DLBCL from Western patients with available immunostainning data for CD10,BCL6,MUM1,GCET1 and FOXP1 were also subclassified by the two algorithms.(2) Conventional cytogenetic analysis was performed on a total of 118 Chinese patients and a total of 216 patients from the University of Nebraska medical center with de novo DLBCL. Immunohistochemical analysis of CD10,BCL6,and MUM1 expression was used to categorize the GCB or non-GCB DLBCL according to Hans algorithm.Interphase fluorescence in situ hybridization(FISH) was used to determine the incidence of the t(14;18) and BCL6 rearrangements.The cytogenetic data were entered into a relational database for further computational analysis.(3) The BCL2 expression was studied on 124 cases of Chinese de novo DLBCL using immunohistochemistry, the cytogenetic alterations in BCL2-positive and BCL2-negative DLBCL patients were also investigated by conventional cytogenetics and interphase fluorescence in situ hybridization(FISH) analysis and the findings were compared to those in a cohort of 114 well-studied DLBCL from Western population.Results:(1) Of 124 DLBCL cases from the Chinese patients,27(22%) cases showed a GCB phenotype whereas 97(78%) cases had a non-GCB phenotype using Hans algorithm and 34(27%) cases were considered GCB and 90(73%) cases were considered non-GCB using Choi algorithm.Of 114 DLBCL cases from the Western countries,60(53%) cases were considered GCB and 54(47%) cases were considered non-GCB using the algorithm of Hans et al.and 64(56) cases were considered GCB and 50(44%) cases were considered non-GCB using the new algorithm developed by Choi et al.(2) The Chinese DLBCL was significantly more frequent in gains of 1q21-q32,3p21-p25,3q21-qter,3,7p10-p15,7q11.2-q22,18,19q12-qter and loss of Y than DLBCL from Nebraska(p＜0.05).The Chinese GCB subgroup was significantly more frequent in gains of 1q41-qter and 11q13-q14 than the Chinese non-GCB subgroup and the Nebraska GCB subgroup was significantly more frequent in gains of 7 and 12 and loss of 17p11.2-p13 than the Nebraska non-GCB subgroup (p＜0.05).The Chinese GCB subgroup was significantly more frequent in gains of 1q and 11q than the Nebraska GCB subgroup(p＜0.05).Both the Chinese and Nebraska non-GCB subgroups were characterized by more frequent gains of 3/3q and 18/18q. Breakpoint of 3q27 and t(3;14)(q27;q32) and its variants were seen in 39%and 20% of Chinese DLBCL cases whereas only 5%and 1%of Nebraska DLBCL cases, respectively(p＜0.05).Breakpoint of 18q21 and t(14;18)(q32;q21) were seen in 26% and 25%of Nebraska DLBCL cases whereas only 5%and 3%of Chinese DLBCL cases,respectively(p＜0.05).Within both Chinese and Nebraska cohorts,the majority of cases with t(14;18) were in GCB subgroup whereas only a few cases were in non-GCB subgroup(p＜0.05).(3) Expression of BCL2 protein was seen in 69% (85/124) of the Chinese DLBCL cases whereas in 50%(57/114) of the Western DLBCL cases(p=0.0054).Within the GCB subgroup,the percentage of cases with BCL2 overexpression in Chinese patients was similar to that in the Western cohort (47%,16/34 vs 48%,31/64).However,the expression of BCL2 protein was more often seen in the non-GCB subgroup in Chinese patients compared to that in the non-GCB subgroup of the Western cohort(77%,69/90,vs 52%,26/50;p=0.005).In the Western DLBCL cases,the percentage of cases with BCL2 overexpression in the GCB subgroup was similar to that in the non-GCB subgroup(p=0.850).However,the expression of BCL2 protein was more frequent in the non-GCB subgroup than that in the GCB subgroup(p=0.0032) in Chinese patients.The t(14;18)(q32;q21) and gains of 18/18q were highly associated with BCL2 expression in both Chinese and Western DLBCL.Moreover,BCL2 expression had a significant association with 3/3q gain in Chinese DLBCL cases whereas this association was less significant in Western patients.Interestingly,the gains of 18/18q and 3/3q accounted for a large proportion of BCL2 positive cases in GCB-DLBCL in Chinese but not in Western patients.Conclusions:(1) The GCB subtype of DLBCL was significantly less common than non-GCB subtype in Chinese patients.The frequency of GCB subtype was much lower and the frequency of non-GCB subyptes was significantly higher in Chinese patients than that in Western DLBCL patients.(2) The cytogenetic profiles of DLBCL in Chinese patients were distinct compared to the Nebraska patients,specifically gain of 1q and 11q in Chinese GCB-DLBCL cases.A very low frequency of the t(14;18) and a high frequency of the BCL6 rearrangements were observed in Chinese DLBCL cases,whereas in Nebraska DLBCL cases,a higher frequency of the t(14;18) and a lower portion of BCL6 rearrangements were seen.(3) The BCL2 overexpression in DLBCL was more frequent in Chinese than that in Western patients(85 of 124 vs 57 of 114,p=0.0054).Like Western DLBCL,the BCL2 expression was associated with gain of chromosome 18/18q in non-GCB subtype in Chinese patients.Moreover, BCL2 expression had a significant association with 3/3q gain in Chinese DLBCL cases whereas this association was less significant in Western patients.Interestingly, the gains of 18/18q and 3/3q accounted for a large proportion of BCL2 positive cases in GCB-DLBCL in Chinese but not in Western patients.