Rituximab Maintenance In Patients with Chronic Lymphocytic Leukemia (CLL) Sustains the Response Obtained After First-Line Treatment with Rituximab Plus Fludarabine, Cyclophosphamide, and Mitoxantrone (R-FCM).
Authors: Bosch Francesc , Villamor Neus , Abrisqueta Pau , Terol María José , González-Barca Eva , González Marcos , Ferrà Christelle , Abella Eugenia , Delgado Julio , Garcia-Marco Jose A , Gonzalez Yolanda , Carbonell Felix , Ferrer Secundino , Monzo Encarna , Jarque Isidro , Muntanola Ana , Constants Mireia , Escoda Lourdes , Montserrat Emili 
Published: October 2019

Abstract
Abstract 1382

The effectiveness of rituximab maintenance in the treatment of CLL has been investigated in a phase II clinical trial that includes two treatment parts. First, patients were given R-FCM up to 6 cycles as induction therapy, achieving an overall response rate of 93% and 46% of CR with negative minimal residual disease (MRD) (Bosch et al. JCO, etc). Second, three months after concluding R-FCM, patients having achieved CR or PR receive rituximab maintenance (375 mg/m2) every three months for two years (up to 8 cycles). We present here the preliminary results of the second part of the study, namely the efficacy of rituximab maintenance. Evaluation of response was performed three months after the last cycle of maintenance and included bone marrow (BM) examination, MRD assessment in peripheral blood and BM by four-color flow cytometry. Patients in whom rituximab maintenance was prematurely interrupted due to toxicity were considered as failures. Fifty-six patients (median age 60 years, 70% female) responding to R-FCM were evaluable for response to rituximab maintenance. Median number of cycles of maintenance given was 8 (range, 3 to 8), 77% of patients completed the entire planned treatment, whereas 91% received 6 or more cycles. Treatment was delayed due to insufficient hematological recovery in 12 cycles (2.7%). Toxicity was mainly hematological, with neutropenia being observed in 31.8% of cycles (Grade 3&4 in 8.9%), thrombocytopenia in 3.4% and anemia in 3.9%. Hypogammaglobulinemia occurred in 38% of patients (low levels of IgA in 50%, IgG in 34%, and IgM in 60%). Eight patients, three of them with hypogammaglobulinemia, experienced grade 3&4 infectious episodes (4 pneumonia, 2 gastrointestinal, 1 myositis, and 1 cerebral abscess). Herpes virus (I/VZ) reactivation was observed in 8 patients. Two patients died due to multifocal leukoencephalopathy and hemophagocytic syndrome, respectively. After rituximab maintenance, 44.6% of patients were in CR MRD negative, 41% in CR, 3.6% in PR, and 10.7% failed to treatment. Failures were due to disease progression (two patients), development of severe neutropenia (two patients), and death (two patients). Among 28 patients that were in CR MRD (-) at the onset of the maintenance part, 19 held the MRD negative status at the end of maintenance, 5 (18%) turned negative into positive MRD (probability of conversion, 40% at 30 months), whereas 4 failed to treatment (2 neutropenia, 1 progression, 1 death). Moreover, 5 of 24 patients (22%) in CR MRD(+) after R-FCM became MRD negative after rituximab maintenance, 17 maintained the CR, one patient achieved a PR, and one patient progressed under maintenance (Table 1). In conclusion, rituximab maintenance after chemoimmunotherapy seems to prolong duration of response and, in some cases, improves the quality of response towards a CR with negative MRD. Maintenance with rituximab had the major benefit in patients in CR with positive MRD. The exact role and the best dosage and treatment schedule of rituximab as maintenance therapy in CLL should be now investigated in randomized clinical trials.

Disclosures:
Bosch: Hoffman La Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Off Label Use: Rituximab is currently not approved as maintenance therapy for patients with chronic lymphocytic leukemia. Garcia-Marco:ROCHE: Consultancy, Honoraria, Research Funding.