End of treatment FDG-PET in primary mediastinal B-cell lymphoma treated with R-chemotherapy: Prognostic indicator and implications for consolidation radiotherapy

The ideal therapeutic regimen in primary mediastinal B-cell lymphoma (PMBCL) is controversial and may include consolidation radiotherapy (RT). An adequate strategy is essential in a population where long-term effects of RT are significant. We evaluated the prognostic value of end-of-treatment (EOT) FDG-PET in 50 patients receiving rituximab and anthracycline-containing chemotherapy and its implications for consolidative RT. Thirty patients (60%) obtained complete metabolic response (CMR), five received consolidation RT. The remaining patients had partial response (14) and progression (6). Of these, 12 received mediastinal RT, six salvage chemotherapy, and two no further treatment. Five-year progression free survival was 100% and 48% (95% CI 30%-77%) in patients with negative and positive EOT FDG-PET, respectively (P < .001). Five-year overall survival for negative and positive EOT FDG-PET was 100% and 67% (95% CI 48%-93%) respectively (P = .001). Within positive EOT FDG-PET cases, an association was found between Deauville score and survival. The negative predictive value (NPV) of EOT FDG-PET for disease relapse/progression was 100% (95% CI 0.88-1.00); the positive predictive value was 47% (95% CI 0.24-0.71). This study demonstrates the importance of metabolic assessment in PMBCL and is relevant for its high NPV. Our data favor the use of EOT FDG-PET for decisions concerning RT.