Prognostic Role of Pre-Radiation Therapy (18)F-Fluorodeoxyglucose Positron Emission Tomography for Primary Mediastinal B-Cell Lymphomas Treated with R-CHOP or R-CHOP-Like Chemotherapy Plus Radiation.

Purpose: To validate, in a monoinstitutional cohort with extended follow-up, that post-rituximab chemotherapy (R-CT) (18)F-fluorodeoxyglucose positron emission tomography ((18)FDG-PET) is a prognostic factor allowing discrimination of primary mediastinal B-cell lymphoma (PMBCL) patients at higher risk for progression after radiation therapy.

Methods And Materials: We analyzed 51 patients, and (18)FDG-PET scans were re-examined evaluating both the Deauville 5-point scale (D5PS) score and the standardized uptake value (SUV) of residual activity, if present. These parameters were then tested by univariate analysis for a potential correlation with progression-free survival (PFS) as the primary study endpoint.

Results: Median follow-up time was 51 months (range, 9-153 months). After R-CT, D5PS score was 1 in 10 (19.6%), 2 in 11 (21.6%), 3 in 7 (13.8%), 4 in 17 (33.3%), and 5 in 6 patients (11.7%). Forty-three out of 51 patients (84.3%) had an SUVmax ≤5, and 8 out of 51 (15.7%) had an SUVmax ≥5. Overall, 6 patients experienced progression or relapse: 1 had a D5PS score 2 (with SUVmax ≤5), and 5 had a D5PS score 5 (and SUVmax ≥5). Patients with a D5PS score 5 showed significantly lower PFS rates versus all other scores (log-rank P<.001), as did patients with SUVmax ≥5 when compared with those with SUVmax ≤5 (log-rank P<.001).

Conclusions: The present study confirmed the prognostic role of (18)FDG-PET after R-CT, with patients with a D5PS score of 5 and/or an SUVmax ≥5 being at high risk of progression/relapse after RT.