Rituximab Plus Chlorambucil As Initial Treatment for Elderly Patients with Chronic Lymphocytic Leukemia (CLL): Effect of Pre-Treatment Biological Characteristics and Gene Expression Patterns on Response to Treatment

Abstract ²⁹⁴

Rituximab plus fludarabine/cyclophosphamide (R-FC) is currently the standard of care for fit patients with untreated or relapsed CLL. However, patients with CLL are predominantly an elderly population and many of these patients may have comorbidities that make them less suitable to receive fludarabine-containing therapy. Chlorambucil-based treatments are frequently used for these patients despite the fact that clinical benefits are limited. There is a need for well-tolerated and more efficacious treatment regimens for these patients.

The ML21445 study evaluated the combination of rituximab and chlorambucil (R-chlorambucil) as first-line treatment for patients with CLL considered ineligible for treatment with the current standard of care, R-FC. Patients aged >65 years (or 60–65 years and ineligible for fludarabine) were treated with eight 28-day cycles of chlorambucil (8 mg/m²/day Days 1–7) with rituximab administered on Day 1 of cycle 3 (375 mg/m²) and cycles 4–8 (500 mg/m²). Patients with a response at the end of induction were randomized to rituximab maintenance therapy (375 mg/m² every 8 weeks for 2 years) or observation. The induction phase of the study is complete while the maintenance phase is still ongoing. The overall response rate (ORR) in 85 patients who received at least one dose of rituximab during induction was 81.2% (n = 69) with 16.5% (n = 14) achieving a complete response (CR) and 2.4% (n = 2) a CR with incomplete bone marrow recovery (CRi). ORR and CR rates were similar across the different Binet stages (ORR: Binet A 86.4%, Binet B 79.6%, Binet C 78.6%) and age categories (ORR: 60–64 years 84.6%, 65–69 years 85.2%, 70–74 years 75.0%, ≥75 years 81.0%). Two of four patients aged ≥80 years responded to induction treatment. Logistic regression analysis revealed no correlation between known biological prognostic factors – CD38, cytogenetics, IGHV mutational status, ZAP-70, thymidine kinase, soluble CD23, and beta-2 microglobulin – and response to treatment. To further investigate possible factors influencing response, pre-treatment patterns of gene expression were analyzed in different patient subgroups. Material was available for 62 patients, including 16 with CR/CRi, 41 partial responders and 5 non-responders. In an exploratory analysis, mRNA expression was examined using Affymetrix® Human Genome U133 microarrays. This revealed marked differences in pre-treatment gene expression profiles between response groups. Non-responders showed a homogeneous gene expression signature involving up-modulation of transcripts involved in anti-apoptotic and pro-proliferative pathways, including K-ras and N-ras. CR/CRi patients also showed a homogeneous pattern of gene expression that was clearly distinct from non-responding patients, while patients with a partial response showed a more heterogeneous pattern of gene expression before treatment.

These initial findings reflect the heterogeneity of CLL and suggest that microarray analysis of gene expression may be useful in predicting response to R-chlorambucil in elderly patients with CLL.