Baseline PET-Derived Metabolic Tumor Volume Metrics Did Not Predict Outcomes in Follicular Lymphoma Patients Treated with First-Line Immunochemotherapy and Antibody Maintenance in the Phase III GALLIUM Study

Introduction: Evidence suggests that baseline ¹⁸fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography-derived parameters, such as metabolic tumor volume (MTV) and maximum standardized uptake value (SUV_max), may predict progression-free survival (PFS) in patients (pts) with follicular lymphoma (FL) treated with first-line R-CHOP immunochemotherapy. However, data from pts routinely treated with bendamustine or antibody maintenance are lacking, and several methods have been used to evaluate PET metrics for tumor burden in pts with lymphoma. This prospective exploratory analysis assessed the prognostic value of baseline MTV, total glycolytic activity (TLG), and SUV_max for PFS and overall survival (OS) in pts with FL treated with first-line obinutuzumab (GA101; G) or rituximab (R) plus chemotherapy (chemo) in the Phase III GALLIUM study (NCT01332968; Marcus et al. N Engl J Med 2017), using two published methods for measuring tumor burden.

Methods: Pts ≥18 years with previously untreated FL (grade 1-3a) and advanced disease (Stage III/IV or Stage II with tumor diameter ≥7cm) requiring treatment were randomized 1:1 to receive 6-8 cycles of G (1000mg intravenous [IV] on days [D] 1, 8, and 15 of cycle [C] 1 and D1, C2-6 or 8) or R (375mg/m² IV on D1) plus standard chemo (CHOP, bendamustine, or CVP). Responding pts received the same antibody as maintenance every 2 months for up to 2 years. After an early protocol amendment, PET imaging at baseline and end of induction (EOI) was mandatory in the first 170 pts and optional thereafter. Independent reviewers segmented FDG-avid tumors applying thresholds of I) standardized uptake value (SUV)_max ≥2.5, and II) SUV_max ≥41% of lesional maximum SUV and a minimum volume of 1mL, using MIM software. Results were analyzed for the PET intent-to-treat population. MTV, TLG, and SUV_max were split into quartiles: Q1, <25%; Q2, 25-49%; Q3, 50-74%; and Q4, 75-100%, based on their distribution in the available population. Investigator-assessed PFS and OS were estimated using Kaplan-Meier methods (data cut-off, February 12, 2018). Hazard ratios refer to stratified log-rank tests comparing Q2, Q3, and Q4 with Q1, adjusted for the randomization stratification factors FLIPI score and chemo regimen. Multivariable Cox analyses were also undertaken to investigate whether baseline MTV quartiles and other covariates were prognostic for PFS. Statistical significance at 0.05 was determined using the Wald test.

Results: Of 1202 enrolled FL pts, 609 had a baseline PET scan and 521 had baseline PET scans available for all quantitative assessments by central review; 303 pts (58%) received bendamustine, 179 (34%) CHOP, and 39 (8%) CVP. After a median follow-up of 57 months, none of the 3 baseline PET parameters (MTV or TLG measured by either method or SUV_max) significantly predicted PFS (Table). Multivariable analysis, which included baseline pt and disease characteristics, confirmed that MTV did not predict PFS. Consistent with the primary analysis, receipt of G-chemo was an independent predictor of improved PFS.

Conclusions: Contrary to previous reports, these prospective data from the Phase III GALLIUM study show that baseline quantitative PET metrics do not predict PFS or OS in FL pts receiving first-line immunochemotherapy (of whom the majority received bendamustine) followed by antibody maintenance treatment, irrespective of the measurement method applied. Conversely, a previously reported analysis from GALLIUM suggests that PET-complete metabolic response at EOI assessed using Lugano 2014 criteria is a strong predictor of long-term outcome in these pts.

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