Transformation to diffuse large B‐cell lymphoma and its impact on survival in patients with marginal zone lymphoma: A population‐based study

Abstract Some patients with marginal zone lymphoma (MZL) experience histological transformation to diffuse large B‐cell lymphoma (DLBCL). Because of the paucity of long‐term data on transformation, we conducted a population‐based study to estimate the risk of transformation and its impact on survival in MZL. Using the Surveillance, Epidemiology and End Results database, we identified 23 221 patients with histology‐proven MZL between 2000 and 2018. Competing risk method, Kaplan‐Meier and Cox proportional hazards regression were performed to analyze time‐to‐event outcomes. Based on 420 events of transformation, the 10‐year cumulative incidence rate of transformation is 2.23% (95% CI: 2.00%‐2.46%) in MZL, 1.5% (95% CI: 1.3%‐1.8%), 2.7% (95% CI: 2.3%‐3.2%) and 5.8% (95% CI: 4.6%‐7.1%) in extranodal, nodal and splenic MZL (EMZL, NMZL and SMZL), respectively. Patients with SMZL (subdistribution hazard ratio [SHR], 2.96; 95% CI: 2.21‐3.96) or NMZL (SHR, 1.49; 95% CI: 1.17‐1.90) have a higher risk of transformation than those with EMZL. For each MZL subtype, patients with transformation had a significantly shorter overall survival. Patients with transformation >18 months since MZL diagnosis had longer OS than those who presented within 18 months (5‐year rate, 87.4% [95% CI: 83.7%‐91.2%] vs 47.9% [95% CI: 38.8%‐59.0%]; P < .001). Compared to patients with matched de novo DLBCL, those whose DLBCL was transformed from MZL had a shorter OS (5‐year rate, 56.6% [95% CI: 51.9%‐61.8%] vs 46.1% [95% CI: 40.9%‐51.9%]; P < .001). We concluded that patients with SMZL had the highest risk of transformation. Regardless of MZL subtype, transformation resulted in significantly increased mortality.