Minimal Residual Disease and IGHV-Genes Mutational Status as the Main Predictors of Response to Bendamustine-Rituximab Therapy in Previously Untreated Chronic Lymphocytic Leukemia

Abstract

Background. In patients with chronic lymphocytic leukemia (CLL) the eradication of minimal residual disease (MRD) is a prognostic factor of overall survival (OS) and progressionfree survival (PFS). IGHV mutational status has also independent prognostic value. Aim. To analyse the impact of mutational status and MRD eradication in CLL patients after first-line standard BR (ben-damustine + rituximab) immunochemotherapy. Materials & Methods. The prospective study included patients with immunophenotypically confirmed CLL who had not previously received anticancer therapy. All patients were treated by BR combination from 2012 to 2015. MRD level was determined in 109 patients after completing the 3<sup>rd</sup> and the 6<sup>th</sup> treatment courses. IGHV mutational status data were available for 98 patients. IGHV mutational status was evaluated in accordance with ERIC recommendations. MRD was assessed by standardized method of 4-color flow cytometry. Results. MRD negativity was achieved in 37 (34 %) out of 109 patients. MRD eradication correlated with the best PFS (p = 0.04). IGHV mutational status had a statistically significant impact on PFS (p = 0.02). In patients with MRD-nega-tive response and IGHV mutation no unfavorable events occurred during the period of monitoring. Conversely, PFS rates in MRD-negative patients having no IGHV mutation and in MRD-positive patients with mutation were significantly worse. MRD eradication resulted in statistically significant improvement of PFS rates after completing 3 treatment courses, compared with the cases with MRD persistence regardless of residual malignant clone level (p = 0.01). Conclusion. BR therapy as first-line treatment statistically improved PFS in patients who achieved MRD-negative remission after completing the 3<sup>rd</sup> treatment course. PFS was significantly higher in MRD-negative patients with IGHV mutation after 6 treatment courses. MRD negativity resulting from 6 BR therapies in patients having no / GHV mutation was not accompanied by PFS improvement. It follows that by itself MRD negativity cannot be considered to be a universal prognostic factor.