Key Ideas

Frontline treatment for mantle cell lymphoma (MCL) is no longer a simple, one-size-fits-all algorithm split by transplant eligibility; it now requires weighing chemotherapy-free options, BTK inhibitor combinations, and, increasingly, a genuinely chemotherapy-free triplet regimen for both younger and older patients. In the relapsed setting, non-covalent BTK inhibitors, next-generation BCL2 inhibitors, CAR T-cell therapy, and bispecific antibodies now offer a real, defined sequence of options after covalent BTK inhibitor failure.

Rethinking a Once-Simple Algorithm

Frontline treatment for MCL used to follow a fairly simple path: young, fit patients eligible for transplant received intensive induction chemoimmunotherapy, autologous stem cell transplant, and rituximab maintenance, while patients not fit for transplant received bendamustine-rituximab (BR) induction followed by rituximab maintenance. The central question the field has been asking for several years now is whether that framework can be improved upon.

One strategy has been adding a BTK inhibitor to the BR platform. The phase 3 ECHO trial, adding acalabrutinib to BR followed by acalabrutinib maintenance versus placebo plus BR, was positive for its primary endpoint, progression-free survival; overall survival was not statistically significant, though the trend was in the right direction. That result supported acalabrutinib's approval in the frontline, older-patient setting.

An interesting related question is whether combination therapy is actually required for everyone, or whether a sequential approach, BR first, then a BTK inhibitor at relapse, might work just as well. Comparing progression-free survival from the acalabrutinib combination approach against a sequential BR-then-BTK-inhibitor strategy, the numbers, while not perfectly matched for direct comparison, look fairly similar in ECHO. That suggests a subset of older patients may not need combination therapy upfront and could reasonably start with BR alone, reserving a BTK inhibitor for the second line.

Another strategy has been going chemotherapy-free entirely. The ENRICH trial, a UK study, compared ibrutinib-rituximab against investigator's choice of BR or R-CHOP in older patients, and met its primary endpoint of progression-free survival. Looking at subgroups, ibrutinib-rituximab performed better than R-CHOP specifically, but for patients whose comparator arm was BR, the two regimens performed about the same. 

The practical takeaway is that a chemoimmunotherapy approach is a reasonable initial strategy for older patients, with a BTK inhibitor reserved for the second line in lower-risk patients, while higher-risk patients may benefit from combining a BTK inhibitor with chemoimmunotherapy upfront. For patients not fit for chemotherapy at all, a BTK-inhibitor-based approach alone is a reasonable choice.

Younger, Transplant-Eligible Patients: Rethinking Three Questions

For younger patients, the relevant trial evidence breaks down into three questions: induction regimen, the role of transplant, and maintenance strategy.

On induction: the MCL Younger trial established that a cytarabine-containing induction backbone produces better results than R-CHOP alone. On maintenance: the LyMa trial confirmed that rituximab maintenance after induction improves overall survival. On transplant specifically, the supporting evidence is comparatively weaker; it took a small trial a very long time to show even a marginal overall survival benefit for transplant, and that benefit applied only to patients who did not receive rituximab. Transplant, in other words, currently has the least robust supporting evidence of the three components in this algorithm.

The European TRIANGLE trial directly tested this framework, using a cytarabine-containing induction backbone (R-CHOP alternating with R-DHAP) followed by autologous transplant and rituximab maintenance, transplant with the addition of ibrutinib in induction and maintenance, or an ibrutinib-containing arm without transplant at all. The two ibrutinib-containing arms, with or without transplant, both outperformed the traditional transplant-plus-maintenance approach, and the two ibrutinib-containing arms performed similarly to each other. That suggests that including a BTK inhibitor with induction and maintenance can reduce or eliminate the benefit of adding transplant, and the two ibrutinib-based arms add real weight to the traditional transplant approach falling somewhat behind. This is practice-changing in many countries: a BTK-inhibitor-containing frontline regimen can be used, and transplant can reasonably be omitted.

In the United States, the cooperative groups have approached this differently, largely through two separate trial questions: one addressing induction regimen choice, and one specifically addressing transplant. The induction trial EA4181 compared the BR and R-cytarabine (BR/RC) standard and two experimental arms, one adding acalabrutinib to BR/RC, the other acalabrutinib plus BR. The acalabrutinib-BR arm was actually closed early, at roughly 80% to 85% enrollment, because the data monitoring committee judged it would unlikely outperform the standard arm. Despite that early closure, induction results across all three arms performed quite similarly in terms of complete response rate and progression-free survival, suggesting BTK inhibitor addition to the BR/RC backbone may be unnecessary, though the closed acalabrutinib-BR arm still performed reasonably well and may be an acceptable induction option for younger patients.

The transplant-specific question was addressed by the EA4151 trial, which allowed any induction regimen, then used MRD status to guide randomization: patients achieving complete response and MRD-negative status after induction were randomized to transplant versus no transplant, followed by rituximab maintenance. The results showed that among patients who achieve a complete response with undetectable MRD after induction, transplant can reasonably be omitted.

Putting these pieces together, there are now two reasonable frontline pathways for younger, fit patients: follow either the TRIANGLE model (BTK inhibitor and R-CHOP/R-DHAP induction, no transplant, followed by BTK inhibitor and rituximab maintenance), or the ECOG model (using a cytarabine-based or acalabrutinib-BR induction, followed by MRD-guided transplant, and rituximab maintenance). A hybrid, or “North American TRIANGLE”, approach may be reasonable as well: acalabrutinib-BR induction, no transplant, and acalabrutinib and rituximab maintenance.

Genuinely Chemotherapy-Free Frontline Regimens

The field is also moving toward truly chemotherapy-free frontline options, including BTK-inhibitor/BCL2-inhibitor-based regimens and lenalidomide-based induction. A well-known example is BOVen (zanubrutinib, obinutuzumab, and venetoclax), initially studied specifically in TP53-mutant MCL, a historically difficult-to-treat, high-risk subgroup where standard chemoimmunotherapy typically produces a 20% to 30% two-year progression-free survival. BOVen achieved a remarkable 88% complete response rate, a high MRD-undetectable rate, and a two-year progression-free survival of 72%, comparing very favorably with chemoimmunotherapy in this specific high-risk population. The same regimen and schedule was subsequently tested in transplant-ineligible older patients more broadly (not restricted to TP53-mutant disease), in a cohort of 50 patients, again showing a very high complete response rate, MRD-negative rate, and encouraging two-year outcomes. Other similar triplet regimens have shown excellent efficacy as well.

Before a genuinely triplet, chemotherapy-free regimen like BOVen can be established as frontline standard of care, it will need to be tested directly against a BTK-inhibitor-based chemoimmunotherapy regimen in randomized trials, which are now underway.

Sequencing Options After BTK Inhibitor Failure

Two separate questions define the relapsed setting: how to choose among BTK inhibitors at relapse, and what comes after a covalent BTK inhibitor fails.

For BTK-inhibitor-naive patients (those who received chemoimmunotherapy, transplant, or another approach without ever receiving a BTK inhibitor), multiple trials support the use of covalent BTK inhibitors at that point. Increasingly, though, patients will already have been exposed to a covalent BTK inhibitor by the time they relapse. If a patient received continuous covalent BTK inhibitor therapy and progressed, a non-covalent BTK inhibitor is the appropriate next step, since the disease has already demonstrated resistance to the covalent mechanism. A trickier scenario arises with fixed-duration, covalent BTK-inhibitor-containing frontline regimens like TRIANGLE: a patient may complete treatment and be off therapy entirely for some time before eventually relapsing. Whether to treat "early" versus "late" relapse differently at that point is a reasonable question, but the data to define that distinction don't yet exist. It would be reasonable to try covalent BTK inhibitor for late relapses, while switching to noncovalent BTK inhibitor might be more appropriate for early relapses.

Post-covalent BTK-inhibitor options continue to improve, including CAR T-cell therapy, non-covalent BTK inhibitor (pirtobrutinib), and new BCL2 inhibitor (sonrotoclax); the latter recently gained FDA approval and should be available for use very soon. Bispecific antibody data are not yet approval-level but are already endorsed in NCCN guidelines. 

Briefly summarizing the data on these agents: pirtobrutinib, a non-covalent BTK inhibitor studied in the post-covalent BTK-inhibitor setting via the BRUIN trial, shows an overall response rate approaching 60% and a complete response rate around 20%; a smaller exploratory cohort of 14 BTK inhibitor-naïve patients showed a higher response rate, around 85%, with a complete response rate around 36%. For context, historical data after BTK inhibitor exposure, prior to CAR T-cell therapy or similar options, show overall survival typically only in the six-month range. The pirtobrutinib data represent a meaningfully better outcome in this difficult-to-treat population.

A next-generation BCL2 inhibitor sonrotoclax is also showing encouraging results post-BTK-inhibitor exposure: overall response rate around 50%, with a median duration of response of 16 months. As with the non-covalent BTK inhibitor data, this compares favorably with historical outcomes in a similarly difficult population; real-world data and potentially combination approaches will help define this agent's eventual role.

On available CAR T-cell products: brexucabtagene autoleucel now has five years of follow-up in BTK inhibitor exposed popluation in the ZUMA-2 trial, with a median progression-free survival of approximately 2 years in all comers and a median overall survival of approximately 4 years, supporting its long-term efficacy. When studied in a BTK-inhibitor-naive cohort, brexucabtagene autoleucel showed high response rates and early signs of durability. Lisocabtagene maraleucel also demonstrated excellent efficacy in the TRANSCEND trial, which might have included slightly more patients with comorbidities and reduced fitness, so cross-trial comparison should account for that different population. In terms of response and progression-free survival, the products look numerically similar, but lisocabtagene maraleucel may be a reasonable option for a somewhat less fit patient population, given a comparatively lower rate of high-grade CRS.

On bispecific antibody data specifically: an updated single-arm trial presented this year shows a complete response rate over 70% in the BTK-inhibitor-exposed setting; in the BTK-inhibitor-naive setting, response rate was over 90% and CR rate was 85%. What's particularly encouraging is durability, with long-term follow-up now showing maintained response. A randomized trial confirming this regimen with BR or rituximab and lenalidomide is ongoing, so a formal approval will still take some time. Separately, a polatuzumab vedotin and mosunetuzumab combination was recently published in Blood, also showing high response rates across all-comer populations (around 88% overall response, close to 80% complete response), including maintained response rates in high-risk disease subgroups; longer follow-up will help determine whether this holds up against emerging alternatives.

Summary for Practice Today

For older or unfit, first-line patients, options include BR with or without acalabrutinib, or a BTK-inhibitor-containing, chemotherapy-free approach. For patients not eligible for BR-based chemotherapy, a BTK inhibitor alone is now a reasonable standard. For younger, transplant-eligible patients, use of BTK inhibitors during induction and maintenance is increasingly common, and fewer patients are being transplanted today; that appears to be the emerging standard for the next couple of years. Triplet, chemotherapy-free regimens seem to represent the future, but randomized trials confirming that a triplet actually outperforms chemotherapy-based approaches in the frontline are still needed.

In the relapsed setting, treatment depends heavily on BTK inhibitor exposure status: if a patient is BTK-inhibitor-naive or covalent BTK-inhibitor-sensitive, a covalent BTK inhibitor remains a standard choice. Otherwise, non-covalent BTK inhibitors would be more appropriate. CAR T-cell therapy provides durable responses and should generally be prioritized when feasible, and patients should be referred and evaluated for CAR T-cell therapy early in their relapsed disease course, since earlier referral tends to support better outcomes. New BCL2 inhibitors and bispecific antibodies are becoming available soon, adding meaningful additional options for controlling disease or bridging patients to more definitive therapy.

For Patients

Mantle cell lymphoma (MCL) treatment has become considerably more individualized in recent years, and the right approach depends heavily on a patient's age, overall fitness, and how their disease responds to initial treatment. For younger, healthier patients, treatment decisions now often involve whether to add newer targeted drugs (called BTK inhibitors) to standard chemotherapy, and whether a bone marrow transplant is still needed, a decision that may be guided by how completely the initial treatment worked, checked with a sensitive test for remaining disease called measurable residual disease (MRD) testing. For older or less fit patients, chemotherapy-free combinations using targeted oral drugs are becoming a well-supported alternative choice aside from chemotherapy-targeted oral drug combinations.

If MCL comes back after initial treatment, several newer options are now available or becoming available soon, including newer-generation targeted pills, CAR T-cell therapy (which uses a patient's own engineered immune cells), and antibody-based treatments that redirect the immune system to attack the lymphoma. Which option is best depends significantly on what treatments a patient has already received.

Given how quickly this field is changing, patients with MCL, especially those whose disease has come back after initial treatment, should ask their oncology team about the full range of current options, including clinical trials, since the standard approach continues to evolve from year to year.

Key Takeaways

  • For younger, transplant-eligible patients, the TRIANGLE trial showed that adding a BTK inhibitor to induction and maintenance can replace autologous transplant, while the EA4151 trial showed that transplant can reasonably be omitted in patients who achieve MRD-negative complete response after induction.

  • For older patients, the ECHO trial supports adding acalabrutinib to bendamustine-rituximab, while the UK ENRICH trial supports a chemotherapy-free ibrutinib-rituximab approach as a reasonable alternative to BR in appropriately selected patients.

  • BOVen (zanubrutinib, obinutuzumab, venetoclax), a genuinely chemotherapy-free triplet, has shown strong results in TP53-mutant MCL (72% two-year progression-free survival) and is being tested more broadly, though triplet regimens still need head-to-head comparison against BTK-inhibitor-based chemoimmunotherapy before becoming a frontline standard.

  • In the relapsed setting, choice of therapy depends heavily on prior BTK inhibitor exposure: BTK-inhibitor-naive or covalent BTK inhibitor-sensitive patients can still benefit from a covalent BTK inhibitor, while covalent BTK-inhibitor-exposed patients should be considered for CAR T-cell therapy, non-covalent BTK inhibitors, next-generation BCL2 inhibitors, or bispecific antibodies.

  • Earlier referral for CAR T-cell therapy in the relapsed setting is associated with better outcomes, supporting a general practice of evaluating eligibility early rather than waiting for extensive disease progression.

References

  1. Wang M, Dreyling M, et al. Time to third-line treatment after bendamustine-rituximab with or without acalabrutinib in patients with previously untreated mantle cell lymphoma: Updated analysis of the phase 3 ECHO trial after 50 months of follow-up. Blood. 2025.

  2. Lewis DJ, et al. brutinib and rituximab versus immunochemotherapy in patients with previously untreated mantle cell lymphoma (ENRICH): a randomised, open-label, phase 2/3 superiority trial. Lancet. 2025.

  3. Dreyling M, et al. Ibrutinib combined with immunochemotherapy with or without autologous stem-cell transplantation versus immunochemotherapy and autologous stem-cell transplantation in previously untreated patients with mantle cell lymphoma (TRIANGLE): a three-arm, randomised, open-label, phase 3 superiority trial of the European Mantle Cell Lymphoma Network. Lancet. 2024.

  4. Wagner-Johnston N, et al. Addition or Substitution of Acalabrutinib in Intensive Frontline Chemoimmunotherapy for Patients ≤ 70 Years Old with Mantle Cell Lymphoma: Outcomes of the 3-Arm Randomized Phase II Intergroup Trial ECOG-ACRIN EA4181. Blood. 2024.

  5. Fenske TS, et al. Lack of Benefit of Autologous Hematopoietic Cell Transplantation (auto-HCT) in Mantle Cell Lymphoma (MCL) Patients (pts) in First Complete Remission (CR) with Undetectable Minimal Residual Disease (uMRD): Initial Report from the ECOG-ACRIN EA4151 Phase 3 Randomized Trial. Blood. 2024.

  6. Kumar A, et al. Zanubrutinib, obinutuzumab, and venetoclax for first-line treatment of mantle cell lymphoma with a TP53 mutation. Blood. 2025;145(5):497-507.

  7. Wang M, Munoz J, Goy A, et al. Pirtobrutinib in Covalent Bruton Tyrosine Kinase Inhibitor Pretreated Mantle-Cell Lymphoma. Journal of Clinical Oncology. 2023.

  8. Eyre TA, et al. Phase I/II Study of Sonrotoclax (BGB-11417) Monotherapy in Patients With Mantle Cell Lymphoma Previously Treated With Anti-CD20 Therapy and a Bruton Tyrosine Kinase Inhibitor. Journal of Clinical Oncology. 2026.