Role of Autologous Stem Cell Transplantation in the Context of Ibrutinib-Containing First-Line Treatment in Younger Patients with Mantle Cell Lymphoma: Results from the Randomized Triangle Trial By the European MCL Network

On behalf of the European MCL Network, ML and EH contributed equally

Introduction: In younger patients with mantle cell lymphoma (MCL), the addition of ibrutinib during induction immuno-chemotherapy and as 2-years maintenance with and without autologous stem cell transplantation (ASCT) has shown high efficacy in the 3-arm randomized TRIANGLE trial (Dreyling et al., Lancet 2024), establishing a new standard of care induction treatment and maintenance. However, the efficacy comparison of the two ibrutinib-containing treatment arms with and without ASCT was still ongoing. With prolonged follow-up, we now aim to clarify the role of ASCT in the context of ibrutinib-containing treatment, to confirm the previously observed treatment effects and to perform overall survival (OS) comparisons.

Patients and methods: In 2016, the European MCL Network initiated the randomized, open-label, 3-arm TRIANGLE trial to evaluate the addition of ibrutinib to standard treatment with ASCT (arm A+I) in comparison to the previous standard treatment (arm A) and an ibrutinib-containing treatment without ASCT (arm I). Patients with previously untreated, advanced stage II-IV MCL, up to 65 years, and suitable for high-dose cytarabine and ASCT, were randomized 1:1:1 to the 3 trial arms in 13 European countries and Israel. Study treatment consisted of 6 alternating cycles of R-CHOP and R-DHAP without (arm A) or with ibrutinib added to R-CHOP cycles and as 2 years maintenance (arms A+I, I). ASCT was planned for patients of arms A and A+I responding to induction therapy. Rituximab maintenance was recommended to be applied according to national guidelines in responding patients of each trial arm. For the primary outcome, failure-free survival (FFS), stable disease at the end of induction, progression, or death were counted as events. Three pairwise log-rank tests for FFS were monitored with regular pre-planned interim analyses, each maintaining a one-sided 1.67% significance level. A pre-defined decision criterion based on the statistical significance of the treatment comparisons for FFS was established to determine the future treatment recommendation. In 2022, arm A had failed to show FFS-superiority over I and FFS in arm A+I was shown to be superior to A. OS was a secondary outcome and formal pairwise OS comparisons between treatment arms were pre-planned with interim analyses based on O’Brien-Fleming boundaries to maintain pairwise two-sided 5% significance levels.

Results: Between July 2016 and December 2020, 870 patients were randomized to arms A (n=288), A+I (n=292), and I (n=290). Median age was 57 years (range 27-68), 76% were male, 87% had stage IV, and 58%/27%/15% had low/intermediate/high risk MIPI. After a median follow-up of 53 months, A+I failed to show FFS-superiority over I (3-year FFS A+I: 86% vs. I: 85%; one-sided p=0.28, hazard ratio: 0.87). FFS-superiority of A over I was again not confirmed with 3-year FFS 75% (A) vs. 85% (I; one-sided p=0.9942, hazard ratio: 1.38). In contrast, the retrospectively calculated two-sided p-value on an overall 5% significance level was consistent with FFS-superiority of I over A (p=0.0102). FFS-superiority of A+I over A was again confirmed with 3-year FFS 86% (A+I) vs. 75% (A; one-sided p=0.0034, hazard ratio: 0.64). Compared with arm A (3-year OS 85%), OS was prolonged in arms A+I and I with 3-year OS of 90% in A+I (p=0.0069, hazard ratio 0.61), and 91% in I (p=0.0041, hazard ratio 0.59).

Conclusions: The results confirm superiority of ibrutinib-containing treatment without ASCT (arm I) over ASCT-containing treatment without ibrutinib (arm A) in terms of both, FFS and OS. In the context of ibrutinib- and high-dose cytarabine-containing induction immuno-chemotherapy and ibrutinib maintenance, the addition of ASCT failed to show FFS superiority, while increasing toxicity during maintenance/follow-up. According to the pre-defined decision strategy, ibrutinib+R-CHOP/R-DHAP induction followed by 2 years of ibrutinib maintenance should be the new standard of care in younger MCL patients, thus ending the era of ASCT for MCL patients.