Efficacy of Ibrutinib in Newly Diagnosed Chronic Lymphocytic Leukemia or Small Lymphocytic Lymphoma: A Combined Analysis of Four Phase III Randomized Controlled Trials

Introduction:

Chronic lymphocytic leukemia or small lymphocytic lymphoma (CLL/SLL), the most common adult lymphoproliferative disorder in western countries, is a B-cell malignancy that is treated based on presenting symptoms and stage. The treatment response is highly variable depending on disease stage and mutation profile of the malignant B cells. Bruton tyrosine kinase (BTK) is a downstream B-cell signaling kinase that has been shown to play a major role in B cell survival and proliferation. Hence, BTK inhibitors have become an attractive therapeutic strategy for treatment of CLL/SLL in both newly diagnosed and relapse/refractory setting. Ibrutinib is a potent oral, covalent inhibitor of BTK that has gained wide acceptance in treatment of CLL/SLL. We analyzed phase III trials where ibrutinib was used in newly diagnosed untreated CLL/SLL to examine treatment effects based on disease staging and molecular profiling.

Methods:

We systematically conducted a comprehensive literature search using MEDLINE, EMBASE databases and meeting abstracts from inception through June 2019. Phase III RCTs utilizing ibrutinib in patients with newly diagnosed/ untreated CLL/SLL were incorporated in the analysis. A generic inverse variance method was used to calculate the estimated pooled hazard ratio (HR) for progression-free survival (PFS) with 95% confidence interval (CI). Heterogeneity was assessed with Cochran's Q -statistic. Random effects model was applied.

Results:

Four phase III RCTs (RESONATE-2, iLLUMINATE, E1912 and A041202 studies) with a total of 1,574 patients with newly diagnosed CLL/SLL were eligible. Studies compared ibrutinib+ obinutuzumab vs chlorambucil+ obinutuzumab, ibrutinib vs chlorambucil, bendamustine+ rituximab vs ibrutinib vs ibrutinib+ rituximab, ibrutinib+ rituximab vs fludarabine+ cyclophosphamide+ rituximab, were included in the analysis. The randomization ratio was 2:1 in E1912 study and 1:1 in other studies. The I2 statistic for heterogeneity was 75, suggesting moderate heterogeneity among RCT. The pooled HR for PFS was statistically significant at 0.28 (95% CI: 0.19-0.41; P < 0.0001). The PFS benefit was observed in all Rai stages, either del11q or del17p and unmutated or mutated IGHV status; Rai stage ≤ 2 cohort (HR, 0.29; 95% CI: 0.21- 0.41; P < 0.0001), Rai stage >2 cohort (HR, 0.31; 95% CI: 0.21- 0.46; P < 0.0001), either del11q or del17p cohort (HR, 0.19; 95% CI: 0.12- 0.31; P < 0.0001), unmutated IGHV cohort (HR, 0.18; 95% CI: 0.12- 0.27; P < 0.0001), and mutated IGHV cohort (HR, 0.27; 95% CI: 0.15- 0.49; P < 0.0001).

Conclusions:

Our meta-analysis showed that ibrutinib maintains activity in newly diagnosed untreated CLL/SLL, across all Rai stages, in del11q or del17p and in unmutated and mutated IGHV. The use of ibrutinib should be further explored considering other factors such as overall survival rates, detrimental side effects, and health-related quality of life for the patients. Ibrutinib clearly outlines an effective treatment option, ultimately increasing the quality of care.