B Cell Lymphoma Unclassifiable, with Features Intermediate Between Diffuse Large B Cell Lymphoma and Burkitt Lymphoma and Diffuse Large B Cell Lymphoma NOS with Doble/Triple Translocations: Immunophenotypic Analysis

Background: Diffuse large B-cell lymphoma (DLBCL) is a clinically and molecularly heterogeneous disease. We can identify two subgroups with aggressive clinical course and higher risk of treatment failure after standard therapy: B cell lymphoma unclassifiable (BCLU) with features intermediate between DLBCL and Burkitt lymphoma (BL) and B-cell lymphomas with double/triple translocation (DHL/THL). Previous reports suggest that these types of lymphomas may show a common immunophenotype, providing another tool in the challenge of their diagnosis.

Objetives: To analyze the immnunophenotype (IF) of BCLU and DH/TH lymphomas by multiparametric flow cytometry and compare it with the IF of a series of cases with DLBCL and BL.

Methods: we analyzed the inmunophenotype (four-color flow cytometry on a FACSCalibur flow cytometer) and cytogenetic studies (FISH to detect MYC, BCL2 and/or BCL6 rearrangement) of cases diagnosed of BCLU and DH/TH lymphomas. Control cases of DLBCL and BL were consecutively collected from our database. Fisher`s Exact test was used to compare proportions between two groups. P-values <0.05 were considered statistically significant.

Results: We analyzed 23 controls (14 DLBCL and 9 BL) and 17 cases: 9 DHL (8 BCL2/MYC+ and 1 BCL6/MYC+), 3 THL (BCL2/BCL6/MYC+) and 5 BCLU (1 IGH-MYC+, 3 MYC+ and 1 unknown). Six of the 17 cases (35.3%) had decreased expression of CD19 while this was exceptional in DLBCL (1/10 P=0.073) and BL (0/9 P=0.054). All of the cases were positive for CD20 but with different intensities: only 5.9% expressed high CD20 compared to 42.9% of DLBCL (p=0.021) and 55.6% of BL (P=0.010). Most of the cases (12/17) had intermediate expression of CD20 and only 4/17 had weak expression. CD10 expression was typical in BL (100%) and frequent in the cases (82.4%), while it was only present in 20% of DLBCL (P<0.0001). CD38 expression was high in 100% of BL, 6.3% of the cases and none of DLBCL. It was intermediate in 64.7% of the cases and in 35.7% of DLBCL (P=0.015). BCL2 overexpression was detected in 57.1% of the cases; neither DLBCL nor BL (P= 0.009) had BCL2 overexpression.

Conclusions: We identify a common immunophenotype in DH/TH lymphomas and BCLU: decreased expression of CD19 and CD20, CD10 expression, overexpression of BCL2 and intermediate expression of CD38. This immuphenotype may be useful for identifying cases for confirmatory cytogenetic studies. Larger studies are needed to validate these results.