Ibrutinib and rituximab versus immunochemotherapy in patients with previously untreated mantle cell lymphoma (ENRICH): a randomised, open-label, phase 2/3 superiority trial

BACKGROUND: Ibrutinib, a Bruton tyrosine kinase inhibitor, prolongs progression-free survival when added to immunochemotherapy as first line treatment. The ENRICH trial compared the chemotherapy-free combination of ibrutinib and the anti-CD20 antibody rituximab (ibrutinib-rituximab) with standard immunochemotherapy (R-CHOP [rituximab-cyclophosphamide, doxorubicin, vincristine, and prednisolone] or bendamustine-rituximab) in patients 60 years and older with untreated mantle-cell lymphoma.

METHODS: This randomised, open-label, phase 2/3 superiority trial was performed at 66 sites in the UK, Sweden, Norway, Finland, and Denmark. Patients 60 years and older with untreated mantle-cell lymphoma (Ann-Arbor stage II-IV disease, an Eastern Cooperative Oncology Group performance-status score of 0-2) were randomly assigned to receive either rituximab plus immunochemotherapy or ibrutinib-rituximab in a 1:1 ratio, stratified by investigator choice of immunochemotherapy. Patients randomly allocated to the ibrutinib-rituximab (intervention) group received 560 mg oral ibrutinib daily in combination with six to eight cycles of 375 mg/m2 intravenous rituximab on day 1 of each cycle in the matched schedule of the pre-randomisation choice of immunochemotherapy (every 21 days for R-CHOP or every 28 days for rituximab-bendamustine). R-CHOP comprised 750 mg/m2 of cyclophosphamide, 50 mg/m2 of doxorubicin, and 1·4 mg/m2 vincristine on day 1 of each 21-day cycle, with 100 mg prednisolone on days 1-5 of each cycle. Rituximab-bendamustine comprised 90 mg/m2 of bendamustine on days 1 and 2 of each cycle, in combination with 375 mg/m2 rituximab on day 1 of each cycle. All responding patients in both groups at the end of induction received maintenance rituximab administered every 8 weeks for 2 years, and patients allocated to the intervention group continued ibrutinib until disease progression or unacceptable toxicity. The primary outcome was investigator-assessed progression-free survival, stratified by immunochemotherapy choice and analysed in the intention-to-treat population. The trial was registered with EudraCT (2015-000832-13) and is closed for recruitment.

FINDINGS: Between Feb 15, 2016, and June 30, 2021, 397 patients were randomly allocated to immunochemotherapy (control) or ibrutinib-rituximab (intervention). Of the 397, 107 (27%) were pre-allocated to the immunochemotherapy choice of R-CHOP and 290 (73%) were pre-allocated to rituximab-bendamustine. In total, 198 were allocated to the control group (53 to R-CHOP and 145 to bendamustine-rituximab) and 199 were allocated to intervention. The median age was 74 years (IQR 70-77) for the intervention group and 74 years (70-78) in the control group. 296 patients (75%) were male and 101 patients (25%) were female; ethnicity data were not collected. At a median follow-up of 47·9 months, the median progression-free survival of ibrutinib-rituximab was superior to immunochemotherapy, with an adjusted hazard ratio (HR) of 0·69 (95% CI 0·52-0·90); p=0·0034. For those with pre-randomisation choice R-CHOP, the HR was 0·37 (0·22-0·62), and with bendamustine-rituximab, the HR was 0·91 (0·66-1·25). Across induction and maintenance, 67% of patients assigned to ibrutinib-rituximab and 70% of patients receiving immunotherapy reported grade 3 or above adverse events.

INTERPRETATION: To our knowledge, this is the first randomised trial in untreated mantle-cell lymphoma to demonstrate significant improvement in progression-free survival for ibrutinib-rituximab compared to immunochemotherapy. This study suggests that ibrutinib-rituximab should be considered a new standard of care option for first-line treatment of older patients with mantle-cell lymphoma.

FUNDING: Cancer Research UK (C7627/A17938) and Johnson and Johnson Pharmaceuticals.