LAUSR

Background: Early-stage follicular lymphoma (FL) is usually managed with involved field radiotherapy (IFRT), allowing a complete and long lasting eradication of the disease only in 40-50% of patients (pts). The aim of this multicenter phase II prospective study was to evaluate the role of MRD in identifying pts unlikely to be cured by IFRT, for whom an immunotherapy consolidation could improve outcome. Methods: 110 pts with stage I/II FL were enrolled and treated with 24 Gy IFRT. Peripheral blood (PB) and bone marrow (BM) samples were centralized to the FIL (Fondazione Italiani Linfomi) MRD Network of EuroMRD-certified laboratories. In BCL2/IGH+ pts at baseline by both nested PCR (NEST) and RQ-PCR (RQ) in BM a/o PB, MRD was analyzed after IFRT and every 6 months over a 3-year period. Pts with MRD+ by both NEST and RQ in BM a/o PB after IFRT or who became MRD+ during the follow-up were treated with 8 weekly doses of the anti-CD20 MoAb ofatumumab (OFA). The primary objective of the study was to define the efficacy of immunotherapy in obtaining a negative MRD. Results: Of the 106 evaluable pts, 50 were males. Median age was 55 y (29-83). The FLIPI score was 0 in 59% of pts, 1 in 35%, 2 in 6%. 68% of pts had inguinal site involvement. At baseline, 30% of pts had a BCL2/IGH rearrangement (30 MBR, 1 MBR and mcr, 1 mcr) in BM a/ o PB;the concordance between compartments was 90%. All but one pt achieved a clinical response after IFRT;one additional pt died soon after IFRT of unrelated causes. MRD evaluation after IFRT revealed the persistence of BCL2/IGH+ cells in PB a/o BM in 60% of pts. MRD + pts, either after IFRT (n = 18) or in case of conversion to MRD+ during the follow-up (n = 6), received OFA, obtaining a conversion to MRD-in 22/24 pts (91.7%-CI 73.0-99.0), significantly superior to the expected 50% (Fig). After a median F-U of 38 m, 17 pts who achieved a MRD-with OFA are still negative;5 converted to MRD+ (2 received OFA retreatment, achieving a second MRD-;2 pts were not re-treated due to Sars-Cov2 pandemic;1 relapsed). A clinical relapse or progression was observed in 23 pts: 18 (24.6%) among the 73 “no marker” pts and 5 (15.6%) among the 32 BCL2/IGH+ at baseline (p = 0.3), with no significant difference in PFS (p = 0.25). Two early relapses were observed among the 12 pts who became MRD-after IFRT and 3 among the 24 treated at least once with OFA (1 MRD+, 1 MRD-, 1 converted from MRD-to MRD+). Only 1 Pt relapsed while MRD-after OFA. Conclusions: MRD data indicate that RT alone is often insufficient to eradicate the disease, inducing a MRD-only in 40% of pts, notably long-lasting only in half of them. The primary objective of this study-MRD conversion after immunotherapy-was largely achieved. The strategy of an immunotherapy consolidation after IFRT in MRD+ pts allowed increasing molecular responses. However, this strategy is applicable only to 30% of enrolled pts. A clinical advantage of the MRD driven treatment strategy is suggested although not significan.