Minimal Residual Disease Response at End of Induction and during Maintenance Correlates with Updated Outcome in the Phase III GALLIUM Study of Obinutuzumab- or Rituximab-Based Immunochemotherapy in Previously Untreated Follicular Lymphoma Patients

Introduction: Minimal residual disease (MRD) status reflects depth of response and informs prognosis after first-line therapy in patients (pts) with follicular lymphoma (FL). In the GALLIUM study (NCT01332968), the primary endpoint of investigator (INV)-assessed progression-free survival (PFS) in previously untreated FL pts was significantly improved with obinutuzumab (GA101; G)- versus rituximab (R)-based immunochemotherapy treatment. We previously reported consistently higher MRD response rates with G- versus R-based treatment at the end of induction (EOI) (92% vs 85%, respectively; p=0.0041; Pott et al. ASH 2016). Here we report the correlation of MRD response at EOI with updated PFS data and the results of MRD response assessment during maintenance treatment and follow-up. We also assessed MRD responses and outcome in pts who remained MRD-positive at EOI. Methods: Previously untreated pts aged ≥18 years with FL requiring treatment were randomized 1:1 to receive 6-8 cycles of G (1000mg IV on days [D] 1, 8, and 15 of cycle [C] 1 and D1 of C2-6 or 8) or R (375mg/m2 IV on D1) plus standard chemotherapy (CHOP, CVP, or bendamustine). Responding pts received the same antibody as maintenance every 2 months for up to 2 years. MRD status was assessed by real-time quantitative (RQ)-PCR assays at mid-induction (MI) in peripheral blood (PB), at EOI in PB and bone marrow, at 4-monthly intervals during maintenance in PB, and at 6-monthly intervals during follow-up in PB, and was defined as negative (MRD response) if RQ-PCR and subsequent nested PCR were negative in all samples analyzed at the respective time point. INV-assessed PFS was estimated using Kaplan-Meier methods (data cut-off, February 12, 2018). Pts were included in the various analyses if they had evaluable MRD data and achieved a complete or partial response at EOI. Results: After 57 months' median follow-up, MRD evaluable pts (n=634/1202 randomized FL pts) who had a MRD-negative response at EOI (n=564) continued to have a longer PFS than those who had a MRD-positive response at EOI (n=70; hazard ratio 0.38; 95% confidence interval 0.26, 0.56; p