Prognostic Significance of BCL6 Translocation in Diffuse Large B-Cell Lymphoma Patients Treated with R-CHOP

Translocation of the BCL6 oncogene is the most commonly-detected chromosomal abnormality in diffuse large B-cell lymphoma (DLBCL), but its prognostic significance remains uncertain. BCL6 translocation has been associated with variable outcomes in prior clinical series, and its clinical impact has not been reevaluated since the introduction of rituximab (R). The objective of this study was to determine the prognostic value of BCL6 translocation in DLBCL patients treated with both CHOP and R-CHOP immunochemotherapy.

Methods We included 163 DLBCL patients treated with CHOP (n=72) or R-CHOP (n=73) at the British Columbia Cancer Agency between the years 1999–2002. Formalin-fixed paraffin-embedded diagnostic lymph node specimens were analyzed for BCL6 translocation on tissue microarray (TMA) by fluorescence in situ hybridization (FISH), using commercially available dual-color break-apart probes (Abbott Molecular, IL, USA). Immunohistochemical analysis was performed for BCL6, CD10, and MUM1 expression, and cases were categorized as germinal centre B-cell-like (GCB) or non-GCB using a standard algorithm (Hans, Blood 2004).

Results BCL6 translocation status was evaluable in 145 cases, and was positive (BCL6+) in 26% (37/145). Median age (65 vs. 59 years, p=0.03) and overall IPI score (p=0.03) were higher in the BCL6+ than in the BCL6− subgroup. Presence of BCL6 translocation correlated with non-GCB phenotype by immunohistochemical analysis (p=0.03), and showed no significant association with BCL6 protein expression (p=0.32). Median follow-up duration was 4.8 years (range, 0.1–8.4). BCL6 translocation was associated with a trend toward decreased overall survival (OS) among patients treated with R-CHOP (5-year OS 46.7% vs. 68%, p=0.098), though not among CHOP-treated patients (5-year OS 36.4% vs.49.5%, p=0.393). Kaplan-Meier analysis limited to the BCL6+ subgroup showed no overall survival difference between patients treated with CHOP and R-CHOP (p=0.67).

Conclusions BCL6 translocations are found in approximately 25% of patients with de novo DLBCL. Presence of BCL6 translocation appears to predict unfavorable outcome in DLBCL patients treated with R-CHOP. However, the adverse prognostic impact of BCL6 translocation is confounded by an association with high IPI score and with non-GCB phenotype. Prospective analysis within large clinical trials would help to determine the independent prognostic value of this marker in the rituximab era.