High rate of metabolic complete response after low dose radiotherapy and obinutuzumab in early stage follicular lymphoma: initial results of the gazai study (gla 2018‐3)

Introduction: The FORT trial demonstrated a higher complete remission (CR) rate using 12 × 2 Gy compared to 2 × 2 Gy in Follicular Lymphoma (FL) (67% vs. 47%). This benefit resulted also in an improved progression free survival (PFS). The TROG 99.03 trial and the MIR study showed an improved PFS with the addition of Rituximab to radiation therapy of 30–40 Gy in early stage FL. Preclinical data suggest that the anti-CD20 antibody may act synergistic with radiation therapy and therefore enhance the radiation effect of low dose radiotherapy. The prospective, multicentric phase II GAZAI study of the German Lymphoma Alliance (GLA) investigated the efficacy of low dose radiation therapy (2 × 2 Gy) in combination with the anti-CD20 antibody Obinutuzumab in early stage nodal FL. The primary endpoint was the metabolic complete remission at the end of therapy. Methods: Patients with early stage FL grade 1/2 were recruited in 11 German centers. Ann Arbor stage I or II was confirmed by FDG-PET/CT. Patients received 1000 mg Obinutuzumab flat dose intravenously in weeks 1, 2, 3, 4, 8, 12 and 16. An interim CT scan was performed in week 7 for response evaluation and subsequent treatment planning. Radiation therapy was applied to the initial involved sites (site of diagnostic surgical intervention and PET positive sites) in week 9. The radiation dose was 2 x 2 Gy on two succeeding days. A FDG-PET/CT was performed at the end of therapy in week 18 for evaluation of the metabolic and morphologic response. Minimal detectable/residual disease (MRD) in peripheral blood was monitored at baseline and at week 18 by allel-specific RQ PCR targeting t(14;18) translocations and clonal immunoglobulin heavy chain (IGH) rearrangements. Results: Of 89 patients included in the study, 54 entered the treatment phase showing FDG-PET-positive lymph nodes qualifying for the primary endpoint. At week 18, metabolic CR (Deauville score (DS) <3) was seen in 46/53 patients (87%; one patient only had a CT without FDG-PET). Partial metabolic remission with a DS 3 was seen in 3 patients (6%) and 3 patients showed a DS 4. Morphologic (CT based) CR/CRu according to Cheson 1999 criteria was seen in 21/54 patients (39%) at week 7 and in 49/54 patients (91%) at week 18. Morphologic PR was seen in 17 patients (32%) at week 7 and in 4 patients (7%) at week 18; one patient (2%) showed progressive disease (metabolic and morphologic) outside of the radiation field. 13/54 patients (24%) were initially MRD positive. All but one patient converted to MRD negativity at week 18. Conclusions: Low dose radiation therapy using 2 × 2 Gy in combination with Obinutuzumab is highly effective in early stage FL. Longer follow-up is necessary to investigate if this effectivity also results in a prolonged PFS. Currently, the FORTplus trial is looking for non-inferiority of this regimen in comparison to a conventional radiation dose (12 × 2 Gy) combined with Rituximab. The research was funded by: Roche Pharma Keywords: combination therapies, indolent non-Hodgkin lymphoma, radiation therapy Conflicts of interests pertinent to the abstract K. Herfarth Research funding: Roche Pharma Educational grants: Roche Pharma C. W. Scholz Consultant or advisory role: Roche Pharma Honoraria: Speakers Honoraria Roche Pharma Educational grants: Roche Pharma K. Hübel Consultant or advisory role: Scientific advisory board Roche Pharma Honoraria: Speaker Honoraria Roche Pharma Research funding: Roche Pharma C. Buske Consultant or advisory role: Roche Pharma Honoraria: Roche Pharma Research funding: Roche Pharma J. Dürig Consultant or advisory role: Scientific advisory board Roche Pharma Honoraria: Speakers Honoraria Roche Pharma Educational grants: Roche Pharma G. Lenz Consultant or advisory role: Advisory board Roche Pharma Honoraria: Speakers honoraria Roche Pharma Research funding: Roche Pharma C. Pott Research funding: Roche Pharma M. Dreyling Consultant or advisory role: Roche Pharma Honoraria: Speakers Honoraria Roche Pharma Research funding: Roche Pharma