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-chemotherapy (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), 5 received consolidation RT. The remaining patients had partial response (14) and progression (6). Of these, 12 received mediastinal RT, 6 salvage chemotherapy and 2 no further treatment. Five-year progression free survival (PFS) was 100% and 48% (95%CI 30-77%) in patients with negative and positive EOT FDG-PET respectively (p<0.001). Five-year overall survival (OS) for negative and positive EOT FDG-PET was 100% and 67% (95%CI 48-93%) respectively (p=0.001). 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 radiotherapy.