Radiation Therapy in Primary Mediastinal B-Cell Lymphoma With Positron Emission Tomography Positivity After Rituximab Chemotherapy

PURPOSE: To investigate the role of radiation therapy (RT) in patients affected with primary mediastinal B-cell lymphoma (PMBCL) with residual 18fluorodeoxyglucose positron emission tomography (18FDG-PET)-positive disease after rituximab chemotherapy (R-CT). METHODS AND MATERIALS: Thirty-seven patients treated with R-CT and RT, all with 18FDG-PET scan at diagnosis and before RT, were included. All 18FDG-PET scans were reviewed, and responses were classified according to the Deauville 5-point scoring system. Outcomes measures were overall survival (OS) and progression-free survival (PFS), estimated for the whole cohort and for subgroups according to 18FDG-PET score after R-CT. RESULTS: The median follow-up time was 40.9 months. Three patients were assigned to Deauville score 1 (8.1%), 9 to score 2 (24.3%), 7 to score 3 (19%), 14 to score 4 (37.8%), and 4 to score 5 (10.8%). After RT, all patients with score 3-4 experienced a complete response (CR). Among patients with score 5, 1 was in CR (25%), 2 had persistent positivity (50%), and 1 showed progressive disease (25%). A total of 4 patients experienced progression or relapse: 1 of 33 (3%) with scores 1-4, and 3 of 4 (75%) with score 5. The 3-year OS and PFS of the whole cohort were 89.8% and 88.7%, respectively. OS was significantly different between scores 1-3 and scores 4-5 (100% vs 77% at 3 years, P<.05). Patients with a score of 5 had a significantly worse outcome than did all other patients (OS at 2 years, 33.3% vs 100%). CONCLUSIONS: Approximately 50% of PMBCL patients show residual disease at 18FDG-PET scan after R-CT. RT is able to convert to CR approximately 85% of these patients, but those with a Deauville score of 5 (10%) appear at high risk of progression and death, and they might be candidates for intensified programs.