Early Stage Follicular Lymphoma. Predictive Role of Minimal Residual Disease (MRD) and Impact of MRD-Driven Treatment with Radiotherapy and Rituximab on Clinical Outcome
Authors: Pulsoni Alessandro , Della Starza Irene , Tosti Maria Elena , Cappelli Luca Vincenzo , Annechini Giorgia , Cavalli Marzia , De Novi Lucia Anna , D'Elia Gianna Maria , Grapulin Lavinia , Guarini Anna , Del Giudice Ilaria , Foa Robin 
Published: October 2019

Abstract
Background. In localized follicular lymphoma (FL, stage I-II), BCL2/IGH+ cells can be detected in the peripheral blood (PB) and/or bone marrow (BM) in 66.7% of cases (Pulsoni et al, BJH 2007). We hereby analyzed the prognostic impact of MRD in localized FL and explored the possibility of a MRD-guided therapeutic approach on a series of patients with a long follow-up.
Methods. Between April 2000 and February 2015, 67 consecutive patients with a confirmed histologic diagnosis of stage I/II FL followed at our Center were enrolled in the study. PB and BM samples were collected at enrollment in all patients and investigated by qualitative PCR to identify the presence of a BCL2/IGH rearrangement. Paraffin-embedded lymph nodes (LN) were studied when available. Patients who proved positive at baseline were studied for MRD every 6 months. Real-Time Quantitative PCR (RQ-PCR) was retrospectively performed according to material availability. All patients were treated with involved field radiotherapy (RT) (24-30 Gy); from 2005, patients who were MRD+ after RT received rituximab (R) (375 mg/m2, 4 weekly administration). The median follow-up is 67 months (17-183); 21 patients (31%) have relapsed after a median of 37 months (17-165) from diagnosis.
Results. At baseline, a clonal marker was found by qualitative PCR in 48/67 cases (72%): 36 were MBR+ (54%), 6 mcr+ (9%), 6 showed a minor BCL2 rearrangement (9%), while 19 (28%) were negative. Fifteen of the latter 19 were analyzed by RQ-PCR and 4 proved MBR+. Of the 13 available LNs, 11 showed the same molecular marker identified in the PB/BM; 2 cases, negative in the PB/BM, showed a rearrangement in the LN only. After RT, 40/42 MBR+/mcr+ patients were analyzed: 20 resulted MRD-, while 20 persisted MRD+. Regardless of the post-RT MRD status, an equal number of relapses was recorded in both groups (7 each). R treatment was administered to the 20 MRD+ patients after RT. Sixteen (80%) achieved a MRD- status after R: over time, 7/16 patients converted to MRD+ and 4 relapsed, whilst 9/16 patients (56.2%) remain persistently MRD- and none has relapsed so far.
To evaluate the impact of R, we considered a series of 27 patients MRD+ after RT or who were MRD- and became MRD+ during the follow-up. Of the 19 patients who received R (1 could not be studied), 15 (79%) did not relapse, while of the 8 untreated patients (pre-2005), 6 (75%) relapsed (p=0.025). Progression-free survival (PFS) was significantly longer for R-treated patients (p=0.0412) (Fig. 1).
To define the predictive role of MRD in the entire cohort regardless of post-RT treatment, we considered the 39 patients with molecular follow-up. Thirteen have relapsed: 10/13 (77%) were MRD+ in the follow-up, including the pre-relapse time point, while 3 resulted persistently MRD-. Contrariwise, of the 26/39 patients in continuous remission, 18 (69%) were persistently MRD- while 8 were MRD+ (p=0.015). PFS was significantly better for MRD- patients (p=0.0163) (Fig. 2).
RQ-PCR was performed in 30 MBR+ patients: 17 (57%) showed a tumor burden ≥10-5 and 13 <10-5. Tumor burden at diagnosis predicted the MRD clearance following RT: 9/13 (69%) cases with low tumor burden resulted MRD- after RT compared to 2/17 (12%) cases with high tumor burden (p=0.0027). Contrariwise, tumor burden did not predict the occurrence of relapse.
Conclusions. Early stage FL at diagnosis can have a heterogenous disease extension: 2 of our cases were truly localized, showing a molecular marker only in the LN. However, in most cases the use of combined qualitative approaches, including canonical MBR/mcr and minor rearrangements, together with RQ-PCR has allowed to identify circulating BCL2/IGH+ cells (52/67 cases: 77.6%), despite a negative BM biopsy. RT induced a MRD negativity in 50% of BCL2/IGH+ patients, but this did not impact on clinical outcome. The administration of R in MRD+ patients decreased significantly the risk of a subsequent relapse and improved PFS. Regardless of treatment, MRD positivity during the follow-up is a predictor of relapse and PFS. Tumor burden at diagnosis is associated with MRD clearance after RT. We support the use of a MRD-driven treatment with anti-CD20 monoclonal antibodies in patients with localized FL after RT.
Figure 1 Figure 1.

Disclosures
No relevant conflicts of interest to declare.