PCR-Based Minimal Residual Disease (MRD) Detection Is a Strong Independent Outcome Predictor Also in Rituximab-Intensive Non-ASCT-Based Programs: Results From the ML17638 Multicenter Randomised Phase III Trial for Elderly Follicular Lymphoma (FL) Patients of the Fondazione Italiana Linfomi (FIL)
Authors: Ladetto Marco , Lobetti-Bodoni Chiara , Mantoan Barbara , Evangelista Andrea , Boccomini Carola , Genuardi Elisa , Botto Barbara , Baldini Luca , Rossi Giuseppe , Pulsoni Alessandro , Raimondo Francesco Di , Rigacci Luigi , Pinto Antonello , Petrini Mario , Sacchi Stefano , Rota-Scalabrini Delia , Gugliotta Luigi , Fanin Renato , Gallamini Andrea , Parvis Guido , Specchia Giorgina , Musto Pellegrino , Olivero Barbara , Gamba Enrica , Ciccone Giovannino , Vitolo Umberto 
Published: October 2019

Abstract
Abstract 787

Background:
Many studies support the value of PCR-based MRD detection using the bcl-2-IgH translocation as an outcome predictor in FL but some failed to confirm this observation. Concerns have been raised particularly for programs which are highly Rituximab (Rtx) intensive (with or without maintenance) and non-ASCT-based. The ML17638 study, contained an extensive centralized MRD monitoring program, whose results are here presented.

Patients and methods:
Clinical results of study have been already reported (Vitolo et al, ASH 2011). The program consisted of 4 R-FND courses (Rtx, fludarabine, mitoxantrone, dexamethasone) followed by 4 doses of weekly Rtx. Patients (pts) achieving 3partial response (PR) were randomized to Rtx maintenance (arm A) or observation (arm B). A total of 234 untreated elderly (age 60–75 years) pts at diagnosis were enrolled. With a median follow-up from randomization of 34 months, 3-year PFS and OS were 66% (95%CI:59-72%) and 89% (95%CI:85-93%), with a clear trend in favor of arm A for 2-year PFS (81% vs 69%).
At enrolment, pts were screened for a molecular marker based on the bcl-2/IgH MBR or mcr. If found, pts were tested at 8 fixed timepoints: at month 5 (M5) after 4-R-FND, at the end of induction therapy (M8) and during maintenance/observation and follow-up (M12,M18,M24,M30,M36 and M42) or until relapse. MRD was assessed by both nested PCR (n-PCR) and real time quantitative PCR (RQ-PCR) on BM cells. Methods have been already reported (Ladetto Exp Hematol 2001). RQ-PCR was performed and analyzed according to the Euro-MRD guidelines (Van der Velden Leukemia 2007). The lab performs routine quality controls in the context of Euro-MRD and was blinded to clinical results and radomization arm. The impact of MRD on PFS was evaluated by log-rank tests and Cox models including age, sex, FLIPI, ECOG PS and complete remission (CR). In addition, the effect of PCR negativity on PFS during the whole follow-up period was evaluated by a time-varying covariate included in the models, also considered in a cumulative way (0, 1, 2, 3 or more consecutive PCR-negative timepoints).

Results:
229 of 234 enrolled pts (98%) were screened at study entry. A molecular marker was found in 118 (51.5%). Of these, 9 were excluded due to withdrawal before M5 (7) or inadequate sampling (2). Overall, 800 follow-up samples were expected. Of these, 707 (88%) were received and analysed: 98% of pts were evaluable for 350% of timepoints and 87% for 375%. Pts with and without a marker had identical PFS (61% at 42m for both). Sixty six per cent of pts achieved PCR-negativity after R-FND and 81% at the end of treatment, with a mean tumor burden reduction of 11 natural logaritm after R-FND and a further decrease of 1.6 after the 4 weekly Rtx. At randomization, PCR-positivity rate was similar in the two arms while during and after maintenance pts in Arm A had a lower rate of PCR-positivity (9% vs 17% p=0.02).
The achievement of PCR-negativity by both n-PCR and RQ-PCR at timepoints M8,12,18 and 24 predicted a better PFS (M5 not predictive, M30, 36, 42 have too early follow up for meaningful evaluation). After M8, 2-year PFS was significantly better in PCR-negative than PCR-positive pts: 72% vs 39% (p=0.007, Fig. 1). Achieving a double PCR-negativity at M8-M12 or triple molecular negativity at M8-M12-M18 was associated with a further increase of PFS (82% vs 46% for months 8–12, p=0.001 and 87% vs 53% for months 8–12-18, p=0.001). PCR-negativity at M8 ensured a subsequent better PFS both in CR (p=0.023, HR=0.33, 95%CI: 0.13–0.86) and PR (p=0.074, HR=0.28, 95%CI: 0.07–1.13) pts (Fig. 2).

Disclosures:
Ladetto: Hoffman-La Roche: Consultancy, Honoraria. Rossi:Roche: Honoraria. Musto:Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Gamba:Roche: Employment. Vitolo:Celgene: Honoraria; Janssin-Cilag: Honoraria; Roche: Membership on an entity's Board of Directors or advisory committees.