Prognostic value of PET-CT after first-line therapy in patients with follicular lymphoma: a pooled analysis of central scan review in three multicentre studies

Background The value of F-18-fluorodeoxyglucose (FDG) PET-CT (PET) imaging in response assessment after first-line rituximab chemotherapy for follicular lymphoma has been documented. We analysed the application of the five-point Deauville scale (5PS; used to score FDG uptake on PET images) in a large cohort derived from three studies, to assess the correlation between post-induction PET status and survival in patients with follicular lymphoma. Methods In this pooled analysis, we used data from three multicentre prospective studies of first-line rituximab chemotherapy for patients with high-tumour-burden follicular lymphoma (the PRIMA study, the PET-Folliculaire study, and the Fondazione Italiana Linfomi FOLL05 study). Patients included in this analysis received at least six cycles of rituximab and chemotherapy before response assessment with conventional contrast-enhanced CT and PET low-dose CT (PET). We included only patients who had a PET scan within 3 months of the last dose of induction rituximab. Patient data, including conventional CT-based response assessment, were recorded for all patients undergoing PET review. Scans undergoing central PET review were scored independently by three reviewers according to the 5PS. The primary endpoints were progression-free survival and overall survival according to the 5PS score of post-induction PET scan (ie, positive [>= 4 points] or negative [<4 points]), analysed in the central review population. Findings Between Dec 24, 2004, and Sept 22, 2010, 439 of the patients enrolled in the three studies underwent local PET assessment, 246 of whom had centrally reviewed post-induction scans. 41 (17%) of 246 patients had a positive post-induction PET scan according to a cutoff of 4 or higher on the 5PS, with substantial reporter concordance. With a median follow-up of 54.8 months (IQR 39.7-68.5; range 7.7-90.1), the hazard ratio (HR) for progression-free survival for patients with a positive PET scan versus those with a negative PET scan was 3.9 (95% CI 2.5-5.9; p<0.0001), and for overall survival was 6.7 (2.4-18.5; p=0.0002). For patients with a positive PET scan, 23.2% (95% CI 11.1-37.9) of patients were progression free at 4 years compared with 63.4% (55.9-70.0) of those who had a negative PET scan (p<0.0001); 4-year overall survival was 87.2% (95% CI 71.9-94.5) versus 97.1% (93.2-98.8), respectively (p<0.0001). Conventional CT-based response (ie, complete response or unconfirmed complete response vs partial response) was weakly predictive of progression-free survival (HR 1.7 [95% CI 1.1-2.5]; p=0.017). Interpretation PET-CT rather than contrast-enhanced CT scanning should be considered as a new standard for response assessment of follicular lymphoma in clinical practice, and could help guide response-adapted therapy.