An international confirmatory study of the prognostic value of early PET/CT in diffuse large B-cell lymphoma: comparison between Deauville criteria and ΔSUVmax

The role of interim PET/CT in guiding therapeutic strategies in diffuse large B-cell lymphoma (DLBCL) is debated, mainly because interpretation rules vary among centres. This study aimed to explore the reproducibility and confirm the prognostic value of early PET/CT using the Deauville criteria and Delta SUVmax. This international confirmatory study retrospectively evaluated 114 patients with newly diagnosed DLBCL treated with a rituximab-containing regimen. All patients underwent F-18-FDG PET/CT at baseline (PET0) and after two cycles (PET2), with no therapy change based on the latter. Scans were interpreted by three observers using the Deauville five-point scale and Delta SUVmax between PET0 and PET2 was calculated. Interpretations were evaluated for interobserver agreement and for progression-free survival (PFS) prediction. Median follow-up was 39 months. Early PET/CT was predictive of outcome when interpreted with the Deauville criteria and Delta SUVmax. Using the five-point scale, the overall kappa value was 0.66 with the reference background set in the liver (score a parts per thousand yen4) and interobserver agreement was even better using a 66 % Delta SUVmax cut-off (kappa = 0.83). Moreover, the prognostic value of interim PET was slightly inferior when using a Deauville score a parts per thousand yen4 than when using a 66 % Delta SUVmax cut-off: for the Deauville score the 3-year PFS estimate was 59 % (45-73 %) in PET2-positive patients vs. 81 % (71-91 %) in PET2-negative patients (P = 0.003); for the 66 % Delta SUVmax cut-off the 3-year PFS estimate was 44 % (23-65 %) in PET2-positive patients vs. 79 % (70-88 %) in PET2-negative patients (P = 0.0002). Although the Deauville criteria are valid for assessing the prognostic value of early PET/CT in DLBCL, computation of the Delta SUVmax leads to better performance and interobserver reproducibility, and should be preferred when a baseline scan is available.