Analysis of Prognostic Value of Postinduction PET Response After First-Line Immunochemotherapy for Follicular Lymphoma


Key Points

  • Complete response rates at end of induction differed for CT and PET on IHP criteria, and PET on Lugano criteria.
  • The difference in progression-free survival rates at 2.5 years for complete response vs no complete response was widest with PET on Lugano criteria.

In an analysis of the phase III GALLIUM trial reported in The Lancet Oncology, Trotman et al found that end-of-induction fluorodeoxyglucose positron-emission tomography (PET) after first-line immunochemotherapy appeared to better predict treatment outcomes than contrast-enhanced computed tomography (CT). An interim analysis of the trial showed that obinutuzumab (Gazyva)-based immunochemotherapy plus obinutuzumab maintenance was associated with a significantly improved risk of relapse, progression, or death compared with rituximab (Rituxan)-based immunochemotherapy plus rituximab maintenance, despite similar response rates on end-of-induction CT.

Study Details

In the trial, 1,202 patients were randomly assigned to obinutuzumab-based treatment or rituximab-based treatment. Those with a response on CT at the end of induction received maintenance treatment for up to 2 years with obinutuzumab or rituximab per randomization.

PET was not available at all study sites. The current analysis involves 595 patients who received baseline and postinduction PET (PET population), with CT and PET results analyzed prospectively according to the 2007 International Harmonisation Project Response (IHP) criteria and PET results also analyzed retrospectively according to the 2014 Lugano criteria, all by independent review committee.

CT and PET Outcomes

In the PET population, overall response rates at the end of induction were 90.6% with CT, 86.9% with PET on IHP criteria, and 81.7% with PET on Lugano criteria. Complete response rates were 29.9% with CT and 65.5% with PET on IHP criteria, and the complete metabolic response rate was 75.6% with PET on Lugano criteria.

Progression-free survival at 2.5 years was 90.5% with complete response vs 79.9% without complete response on CT, 87.8% with compete response vs 72.0% without complete response on PET using IHP criteria, and 87.4% with complete metabolic response vs 54.9% without complete metabolic response on PET using Lugano criteria.        

The investigators concluded, “Our results suggest that PET is a better imaging modality than contrast-enhanced CT for response assessment after first-line immunochemotherapy in patients with follicular lymphoma. PET assessment according to Lugano 2014 response criteria provides a platform for investigation of response-adapted therapeutic approaches.”

The study was funded by F. Hoffmann-La Roche.

Judith Trotman, MBChB, of Concord Repatriation General Hospital, University of Sydney, is the corresponding author for The Lancet Oncology article.

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