Primary Mediastinal B-Cell Lymphoma: The Dilemma of Radiotherapy

Introduction: According to the WHO classification, primary mediastinal (thymic) large B-cell lymphoma (PMBCL) is a distinct entity, which has a close relationship with nodular sclerosing classical Hodgkin's lymphoma (cHL) in terms of clinical and molecular characteristics and sharing an excellent prognosis. When PMBCL is treated with R-CHOP, the addition of radiotherapy (RT) turns more than 90% of positron emission tomography (PET) positive cases into complete remissions (CR) and increases 5-year overall survival (OS) to 93%. However, the fear of potential late toxicities due to RT, has led an increasing number of centers to favor more intensive regimens like DA-EPOCH-R without RT. This controversy is deepened by the recent comparison between the latter regime with R-CHOP, unfavorable to the DA-EPOCH-R for toxicity reasons.

Objective: Evaluate the effectiveness and late toxicities of R-CHOP plus RT in our center and secondarily compare these results with the ones obtained in our cHL patients with bulky and early stage disease.

Methods: Retrospective analysis of patients with PMBCL treated between Jan/2007 and Dec/2017 according to clinical characteristics, late toxicities, rate of CR, OS and disease-free survival (DFS) estimated by Kaplan-Meier method.

Results: In 32 patients with a median age of 34 years (23-70), 56% were male, 91% had limited stage and 6% had an unfavorable IPI. The rate of CR was 91% (2 patients needed second line therapy to achieve CR) with 2 relapses (at 6 and 11 months, respectively) rescued with autologous transplantation. Three deaths were recorded due to disease progression. With a median follow-up of 86 months, OS and DFS at 10 years were 91% and 93%, respectively. As for late toxicities, besides 2 cases of severe pulmonary fibrosis, there were no other relevant late toxicities registered. These results overlap those obtained in our cHL patients with bulky and early stage disease treated with Stanford V plus RT with an OS and an event free survival of 93% and 84%, respectively.

Conclusion: These results support PMBCL's excellent prognosis, parallel to that of cHL. Given the low probability of late toxicities with this regimen our data uphold against the therapeutic strategy of more intensive regimens, that have an increased management complexity and are clinically more toxic.