Ibrutinib-Rituximab versus Immunochemotherapy: A Paradigm Shift in First-Line Treatment for Older Mantle Cell Lymphoma Patients

Highlight

• The ENRICH phase 2/3 randomized trial compared oral ibrutinib plus rituximab against standard immunochemotherapy (R-CHOP or rituximab-bendamustine) as first-line treatment in older mantle cell lymphoma (MCL) patients.
• Ibrutinib-rituximab significantly prolonged progression-free survival (PFS) compared to immunochemotherapy, with a 31% reduction in risk of progression or death overall.
• The benefit was pronounced for patients initially designated to R-CHOP, with a 63% risk reduction, whereas no significant advantage was observed in those pre-selected for rituximab-bendamustine.
• Safety profiles were comparable between arms, with approximately 67% versus 70% experiencing grade 3 or higher adverse events, supporting tolerability of the chemotherapy-free approach.

Study Background

Mantle cell lymphoma (MCL) is an aggressive B-cell non-Hodgkin lymphoma predominantly affecting older adults. Historically, standard first-line treatment options have involved immunochemotherapy regimens such as R-CHOP or rituximab-bendamustine, which combine cytotoxic chemotherapy with anti-CD20 monoclonal antibody therapy. However, these regimens can be associated with significant toxicity, limiting their use in older patients, who represent the majority of the MCL population.

Ibrutinib, a Bruton tyrosine kinase (BTK) inhibitor, has shown efficacy in relapsed/refractory MCL by disrupting B-cell receptor signaling pathways critical for lymphoma survival and proliferation. Earlier studies combining ibrutinib with immunochemotherapy demonstrated enhanced progression-free survival, but the potential of a chemotherapy-free regimen combining ibrutinib and rituximab had not been rigorously evaluated in treatment-naive older patients. This unmet need for effective, tolerable first-line therapies in this demographic motivated the ENRICH trial.

Study Design

The ENRICH trial is a randomized, open-label, phase 2/3 superiority trial conducted across 66 centers in the UK and Nordic countries (Sweden, Norway, Finland, Denmark). Eligibility included patients aged 60 years or older with previously untreated mantle cell lymphoma, Ann Arbor stages II-IV, and ECOG performance status of 0-2.

Participants were randomized 1:1 to receive either:

• Control arm: Rituximab plus investigator-selected immunochemotherapy (R-CHOP or rituximab-bendamustine);
• Intervention arm: Ibrutinib (560 mg orally daily) combined with rituximab matched to the investigator’s chosen immunochemotherapy schedule (6-8 cycles).

Following induction, all responders in both arms received maintenance rituximab every 8 weeks for 2 years. The intervention arm patients continued ibrutinib until disease progression or unacceptable toxicity.

The primary endpoint was progression-free survival (PFS), assessed by investigators and stratified by pre-randomization immunochemotherapy choice. Secondary endpoints included overall survival, safety, and tolerability.

Key Findings

Between February 2016 and June 2021, 397 patients were enrolled and randomized: 198 to immunochemotherapy (53 R-CHOP, 145 rituximab-bendamustine) and 199 to ibrutinib-rituximab. Median age was 74 years, with a predominance of males (75%). The median follow-up was 47.9 months.

Progression-Free Survival

The study demonstrated a statistically significant improvement in PFS with ibrutinib-rituximab compared to standard immunochemotherapy:

• Overall median PFS: HR 0.69 (95% CI: 0.52-0.90), p=0.0034, indicating a 31% reduction in progression or death risk.
• For patients pre-allocated to R-CHOP, HR: 0.37 (0.22-0.62), implying a 63% risk reduction favoring the intervention arm.
• Among those pre-allocated to rituximab-bendamustine, HR was 0.91 (0.66-1.25), showing no significant PFS difference.

Safety Profile

Grade 3 or higher adverse events occurred in 67% of patients in the ibrutinib-rituximab group and 70% in the immunochemotherapy group, indicating comparable tolerability. Detailed adverse event profiles were not disclosed but suggest manageable toxicity with the chemotherapy-free regimen.

Clinical Implications

The ENRICH trial provides compelling evidence that a chemotherapy-free regimen combining ibrutinib with rituximab can improve PFS for older patients with untreated mantle cell lymphoma, particularly those considered for R-CHOP. This translates into a potential new standard of care that minimizes chemotherapy-associated morbidity without compromising efficacy.

Expert Commentary

These findings are practice-changing in the management of older MCL patients who often struggle to tolerate intensive immunochemotherapy. Ibrutinib’s targeted BTK inhibition aligns with precision oncology principles, reducing systemic toxicity while enhancing disease control.

Limitations include the open-label design, which may introduce reporting bias, and the predominant Nordic/UK population which could affect global generalizability. Additionally, the lack of ethnicity data limits understanding of potential racial disparities.

Mechanistically, ibrutinib disrupts survival signaling while rituximab mediates targeted B-cell depletion; their synergy may underlie the improved outcomes documented. Future research should explore long-term overall survival benefit, quality of life measures, and cost-effectiveness.

Conclusion

The ENRICH trial establishes the superiority of ibrutinib plus rituximab over conventional immunochemotherapy in prolonging progression-free survival in older mantle cell lymphoma patients, especially those selected for R-CHOP. This chemotherapy-free approach offers a new therapeutic paradigm with a more favorable safety profile, supporting its adoption as a first-line treatment option. Further studies are warranted to evaluate durability, long-term outcomes, and integration with emerging therapies.

References

Lewis DJ, Jerkeman M, Sorrell L, Wright D, Glimelius I, Poulsen CB, Pasanen A, Rawstron A, Wader KF, Morley N, Burton C, Davies AJ, Lagerlöf I, Dalal S, De Tute R, McNamara C, Crosbie N, Toldbod HE, Sanders J, Allgar V, Aroori S, Warner M, Scully C, Wainman B, Christensen JH, Riise J, Sonnevi K, Bishton MJ, Eyre TA, Rule S; ENRICH investigators. Ibrutinib and rituximab versus immunochemotherapy in patients with previously untreated mantle cell lymphoma (ENRICH): a randomised, open-label, phase 2/3 superiority trial. Lancet. 2025 Oct 3:S0140-6736(25)01432-1. doi: 10.1016/S0140-6736(25)01432-1. Epub ahead of print. PMID: 41052510.