Prognostic significance of B-cell differentiation genes encoding proteins in diffuse large B-cell lymphoma and follicular lymphoma grade 3

Aim

To define prognostic significance of B-cell differentiation genes encoding proteins and BCL2 and BCL6 gene abnormalities in diffuse large B-cell lymphoma and follicular lymphoma grade 3 with >75% follicular growth pattern.

Methods

In 53 patients with diffuse large B-cell lymphoma and 20 patients with follicular lymphoma grade 3 with >75% follicular growth pattern the following was performed: 1) determination of protein expression of BCL6, CD10, MUM1/IRF4, CD138, and BCL2 by immunohistochemistry; 2) subclassification into germinal center B-cell-like (GCB) and activated B-cell-like (ABC) groups according to the results of protein expression; 3) detection of t(14;18)(q32;q21)/IgH-BCL2 and BCL6 abnormalities by fluorescent in situ hybridization in diffuse large B-cell lymphoma and follicular lymphoma grade 3 with >75% follicular growth pattern as well as in GCB and ABC groups; and 4) assessment of the influence of the analyzed characteristics and clinical prognostic factors on overall survival.

Results

Isolated BCL6 expression was more frequently found in follicular lymphoma grade 3 with >75% follicular growth pattern than in diffuse large B-cell lymphoma (P = 0.030). There were no differences in BCL2 and BCL6 gene abnormalities between diffuse large B-cell lymphoma and follicular lymphoma grade 3 with >75% follicular growth pattern. Diffuse large B-cell lymphoma and follicular lymphoma grade 3 with >75% follicular growth pattern patients were equally distributed in GCB and ABC groups. t(14;18)(q32;q21) was more frequently recorded in GCB group, and t(14;18)(q32;q21) with BCL2 additional signals or only BCL2 and IgH additional signals in ABC group (P = 0.004). The GCB and ABC groups showed no difference in BCL6 gene abnormalities. There was no overall survival difference between the patients with diffuse large B-cell lymphoma or follicular lymphoma grade 3 with >75% follicular growth pattern, however, GCB group had longer overall survival than ABC group (P = 0.047). Multivariate analysis showed that BCL6, CD10, and BCL2 expression, BCL2 and BCL6 abnormalities, and International Prognostic Index were not significantly related to overall survival.

Conclusion

Patients with diffuse large B-cell lymphoma and follicular lymphoma grade 3 with >75% follicular growth pattern have very similar characteristics and their prognosis is more influenced by protein expression of B-cell differentiation stage genes than by tumor cells growth pattern, BCL2 and BCL6 abnormalities, and International Prognostic Index.The World Health Organization (WHO) classification defines diffuse large B-cell lymphoma as a specific type of mature B-cell neoplasm (1). However, diffuse large B-cell lymphoma types show clinical, morphological, immunophenotypic, and cytogenetic heterogeneity (2-7). Clinical heterogeneity of diffuse large B-cell lymphoma is a consequence of the expression of B-cell differentiation stage genes. The gene expression analysis has identified three prognostically significant molecular subtypes of diffuse large B-cell lymphoma as follows: germinal center B-cell-like (GCB), activated B-cell-like (ABC), and type 3 diffuse large B-cell lymphoma, which express neither genes of normal GCB-cells nor genes that are normally induced during in vitro activation of peripheral blood B-cells (8-10).Immunohistochemical subclassification of diffuse large B-cell lymphoma showed that GCB and ABC groups greatly differ (11-19). Immunohistochemical GCB and ABC groups are not always considered to be prognostically significant predictors (16-19).Cytogenetic analysis showed t(14;18)(q32;q21)/IgH-BCL2 to be more common in GCB than in ABC (20-24).Follicular lymphoma is the second most common non-Hodgkin B-cell lymphoma (B NHL) (1,25). Follicular lymphoma grade 3, in contrast to indolent follicular lymphoma grade 1 and follicular lymphoma grade 2, is clinically aggressive and has more in common with diffuse large B-cell lymphoma (5).The morphological subtypes of follicular lymphoma grade 3, follicular lymphoma grade 3A, and follicular lymphoma grade 3B show morphological, immunohistochemical, and cytogenetic characteristics of variable clinical importance (1). Clinicopathologic evaluation revealed no differences in survival between follicular lymphoma grade 3A and follicular lymphoma grade 3B patients, yet follicular lymphoma grade 3 cases with a predominant diffuse component (>50%) had a significantly worse survival (25-27).Follicular lymphoma grade 3 is characterized by variable CD10 and BCL2 protein expression and cytogenetic abnormalities, ie, rearrangements of BCL6 gene, BCL2 gene amplification, and less common t(14;18)(q32;q21) (28). Both t(14;18)(q32;q21) and BCL2 protein expression are more common in follicular lymphoma grade 3A, while BCL6 gene rearrangements are more common in follicular lymphoma grade 3B (29-32).Therapy and prognosis of patients with diffuse large B-cell lymphoma and follicular lymphoma are defined according to their morphological characteristics, clinical stage, and clinical prognostic factors included in the International Prognostic Index (IPI) (33,34).The aim of this study was to determine whether follicular lymphoma grade 3 with >75% follicular growth pattern is part of the morphological, immunophenotypic, and cytogenetic spectrum of diffuse large B-cell lymphoma. For that purpose, we determined the following parameters: 1) protein expression of B-cell differentiation stage genes BCL6, CD10, MUM1/IRF4, CD138, and BCL2 expression in patients with diffuse large B-cell lymphoma and lymphoma grade 3; 2) subclassification into GCB and ABC groups according to the results of protein expression profile; 3) t(14;18)(q32;q21)/IgH-BCL2 and abnormalities of BCL6 gene in diffuse large B-cell lymphoma and follicular lymphoma grade 3 with >75% follicular growth pattern, as well as in GCB and ABC groups; and 4) the influence of protein expression, cytogenetic abnormalities, and clinical prognostic factors of age, sex, Ann Arbor clinical stage, and IPI risk group on overall survival (35,36).