EARLY STAGE Follicular Lymphoma: First Results of the FIL "Miro" Study, a Multicenter Phase II Trial Combining Local Radiotherapy and MRD-Driven Immunotherapy

Introduction

Limited stage follicular lymphoma (FL) is usually managed with involved field radiotherapy (IFRT), although different approaches are currently carried out, ranging from watch and wait to combined treatment. RT on involved lymph nodes allows eradication of the disease only in 40-50% of patients. Anti-CD20 monoclonal antibodies (MoAb), widely used in advanced stage FL, are likely to be effective in reducing the relapse risk, although no scientific evidence of their role has been provided. The aim of this multicenter phase II prospective study was to evaluate the role of MRD in identifying patients unlikely to be cured by RT, for whom an immunotherapy-based consolidation could improve outcome.

Methods

110 patients with stage I/II FL were enrolled. IFRT was administered to all patients at a dose of 24 Gy. Peripheral blood (PB) and bone marrow (BM) samples were centralized to the Italian FIL (Federazione Italiani Linfomi) MRD Network of EuroMRD-certified laboratories: the presence of a BCL2/IGH rearrangement was investigated at baseline in all patients by nested PCR (NEST) and RQ-PCR (RQ), the latter according to the EuroMRD guidelines. In patients BCL2/IGH+ at baseline by both NEST and RQ in BM and/or PB, MRD was analyzed in both tissues after IFRT and every 6 months over a three-year follow-up period. Patients with positive MRD by both NEST and RQ in BM and/or PB after IFRT or who became positive during the follow-up were treated with 8 weekly doses of the anti-CD20 MoAb ofatumumab. The primary objective of the study was to define the efficacy of immunotherapy in obtaining the disappearance of BCL2/IGH rearranged cells.

Results

Preliminary data are available for 107 patients, 57 males, 50 females. Median age was 55 years (29-83). 17% had G1 FL, 32% G2, 40% G3A, 11% NOS. The FLIPI score was 0 in 59% of patients, 1 in 35%, 2 in 6%. 69% of patients had inguinal site involvement. Despite a negative BM biopsy, at baseline 30% of patients (n=32) had a BCL2/IGH rearrangement (30 MBR, 1 MBR and mcr, 1 mcr) in the BM and/or PB; the concordance between compartments was 90%, with 10% of negative PB showing a positive BM. No significant differences were observed in relapse probability between patients with or without a molecular marker. All patients were submitted to IFRT and all obtained a clinical response, which was complete in 79 of the 101 evaluated patients (78%) and partial in 22 (22%). MRD evaluation after treatment revealed the persistence of BCL2/IGH rearranged cells in the PB and/or BM in 60% of patients. According to the design of the protocol, MRD-positive patients, either after IFRT (n=18) or in case of conversion to a positive signal during the follow-up (n=7), received 8 weekly administration of ofatumumab. A conversion to MRD negativity, evaluated in 23 treated patients, was obtained in 20 (87% - CI 65.1-97.1). This result was significantly superior to the expected 50%. One death occurred after IFRT, due to ischemic stroke. Adverse events likely correlated to ofatumumab occurred in 7/25 treated patients, consisting of infusion reactions in 5, leading to a permanent interruption of immunotherapy in 3.

After a median follow-up of 18 months, all patients who achieved a MRD negativity with ofatumumab underwent a regular molecular follow-up and are still MRD-negative. Overall, clinical relapse or progression were observed in 17 patients: 13 (18%) among the 73 "no marker" patients; 2 relapses (16%) were observed among the 12 MRD-negative patients after IFRT and 2 relapses were observed among the 23 patients treated with the anti-CD20 MoAb (8.7%), 1 having achieved a MRD negativity and 1 not. No significant differences in event-free survival have so far been observed between the three groups.

Conclusions

The MRD data of this phase II trial for early stage FL indicate that RT alone is often insufficient to eradicate the disease, being capable of inducing a negative MRD only in 40% of evaluable cases, with a long-lasting effect only in half of them. The primary objective of this study - MRD negativity after immunotherapy - was achieved, obtaining the disappearance of BCL2/IGH rearranged cells in the majority of patients treated with ofatumumab. The strategy of an immunotherapy consolidation after IFRT in MRD-positive patients allowed to increase molecular responses. A longer follow-up and further studies on larger patient populations will allow to conclusively define the impact of this MRD-driven strategy also on clinical outcome.