Assessment of Minimal Residual Disease Levels in B-CLL After Front-Line Treatment with FC-R and Rituximab Maintenance

To prospectively analyze change over time in minimal residual disease (MRD) in a cohort of 84 untreated patients diagnosed with CD20+ B-CLL who received from October 2007 to December 2010 six cycles of R-FC (Rituximab 375 mg/m² IV in cycle 1 and 500 mg/m² in cycles 2–6; F: 25 mg/m², and C: 250 mg/m² on days 1–3; every 28 days). Patients who achieved response were treated with rituximab 375 mg/m² every 2 months for 3 years.

EDTA-anticoagulated peripheral blood (PB) and bone marrow (BM) samples were taken at diagnosis, after 3 and 6 cycles of R-FC, and every 6 months during the maintenance phase. MRD was centrally assessed by four-color multiparameter flow cytometry using the following antibody combinations: CD22/CD23/CD19/CD5, CD81/CD22/CD19/CD5, CD20/CD38/CD19/CD5, and CD20/CD79b/CD19/CD5. An acquisition was performed by selection of CD19+ cells/SSC including at least 200,000 events, reaching a sensitivity level of 0.01% (10-4).

PB/BM samples for assessing MRD were available from 28 of the 84 patients after 3 cycles of R-FC and from 79 patients after the 6 induction cycles, and 43 (58%) of the 74 patients on maintenance reached the interim study at 18 months of maintenance (9 cycles). Correlation between PB and BM was 57%, 68%, and 86% at the three study time points. After three R-FC cycles, 16 patients (56.8%) had a MRD- in PB, but only 4 patients (14%) also had MRD- in BM. After six R-FC cycles, 58 patients (73.3%) had a negative study in PB, and 41.7% also in BM. Among the 24 patients analyzed after the third cycle with BM+, 11 achieved negativization after 6 cycles, and MRD was negative in PB in 10 of 12 patients. After 18 months of maintenance, 11 patients (26.2%) converted to MRD- in PB/BM, and a single patient (2.4%) converted to MRD+.

Six cycles of R-FC achieved better MRD- rates in PB and BM as compared to 3 cycles. Addition of rituximab as maintenance after R-FC increased the number of MRD-negative in BM, and in consequence the MRD-negative CRs. A good correlation was not found between MRD values in blood and bone marrow in the induction phase. However, these levels improved in the maintenance phase due to an increase in the number of cases with RMD-negative in BM witch were negatives in PB during induction phase.

Off Label Use: R in Maintenance.