What were the most exciting mantle cell lymphoma (MCL) updates from the recent meeting of the American Society of Hematology (ASH)?
Dr. Martin: The 2022 ASH meeting reported mostly about MCL research, which is great for the MCL community, because clearly, there is a lot of room for improvement. One of the big trials presented at a plenary session—one which we have been eager to see the results from, but maybe did not expect to see quite so soon—was the European MCL Network TRIANGLE trial . This is a 3-arm trial in which 870 patients were randomized. They had treatment-naive MCL and were younger than 66 years, so they were eligible for more intensive chemotherapy.
Arm A was the standard-of-care arm, defined by the prior European MCL Network TRIANGLE Trial. This was 6 alternating cycles of R-CHOP (rituximab, cyclophosphamide, hydroxydaunorubicin hydrochloride [doxorubicin hydrochloride], vincristine, and prednisone) and R-DHAP (rituximab, dexamethasone, cytarabine, cisplatin) – 3 of each followed by autologous stem cell transplant. Arm B was the same regimen with the addition of the first-in-class Bruton tyrosine kinase (BTK) inhibitor ibrutinib to induction followed by 2 years of ibrutinib maintenance. Arm C was the same induction regimen (6 alternating cycles of R-CHOP and R-DHAP plus ibrutinib during induction and maintenance) with no autologous stem cell transplant. Roughly half the patients in the trial, all equally distributed across all arms, received 3 years of maintenance rituximab.
The primary outcome was failure-free survival (FFS). After only 31 months of median follow-up, the trial reported a significant difference in FFS between patients receiving ibrutinib (Arms B and C) and patients who underwent autologous stem cell transplant and did not receive ibrutinib (Arm A).
This clearly shows that 2 years of ibrutinib maintenance significantly improves FFS. FFS was 88% versus 72% (Arm B vs Arm A) at 3 years with a hazard ratio of 0.5. That is a striking hazard ratio, highly statistically significant. Importantly, patients in Arms B and C fared similarly, suggesting that transplant was unnecessary in patients receiving ibrutinib.
What these findings suggest is that in the patient population treated with intensive induction, we are moving beyond autologous stem cell transplant. These results were similar across all subgroups. In fact, outcomes were most striking for patients with higher risk features like high Ki-67 and overexpression of p53.
The patients who need ibrutinib most were those who were most likely to benefit, and that is really encouraging for all of us. There is a clear trend toward an improvement in overall survival with ibrutinib maintenance and there clearly is less toxicity and less treatment-related mortality from avoiding transplant.
It will be important to see this trial published in a peer-reviewed journal with more granular data. But to me, these trial results are groundbreaking. It is a practice-changing trial for sure.
Is there anything else from an investigational approach on the horizon for MCL?
Dr. Martin: Yes. I would like to highlight 2 trials that stand out to me.
First, my colleague Dr. Ruan from Cornell presented on a phase 2 trial of a triplet of acalabrutinib plus lenalidomide plus rituximab with real-time monitoring of minimal residual disease (MRD) in patients with treatment-naive MCL.
This was a small trial with just 24 patients. It was fairly evenly split between low-, medium-, and high-risk MCL international prognostic index (MIPI) scores. All of these patients received the triplet for 1 year of induction followed by an additional year of maintenance with a slightly lower dose of lenalidomide. At the end of 2 years, patients who were in a durable MRD-negative state could stop the oral therapy and just continue with rituximab maintenance.
In a prior trial published in The New England Journal of Medicine , we showed that the lenalidomide plus rituximab regimen has a complete response rate of about 60%. In this new ongoing trial regimen of acalabrutinib plus lenalidomide plus rituximab, we found that at the end of just 1 year of induction treatment, the complete response rate was 83%. With all of the caveats and comparing across trials, this new regimen was clearly active and potentially more active than the prior regimen. It also appeared to be well tolerated without any real significant issues.
I think what this trial plus the TRIANGLE showed us is that BTK inhibitors belong in the front-line setting. That is what patients want. That is what physicians want.
The other trial that I wanted to highlight is an update of something that we saw last year at ASH, specifically a phase 1/2 trial of glofitamab in people with previously treated MCL. The overall response rate was 83% and the complete response rate was 73%. The complete response rate at the first assessment was already almost 50%. These are among patients who have had prior treatment for MCL, including BTK inhibitors.
We are not accustomed to seeing treatments that are so active in the relapsed/refractory MCL patient population, particularly, if they have had a prior BTK inhibitor. So, these results are exciting and promising.
This compares to the ZUMA-2 trial with CAR T-cells. CAR T-cells are also strikingly active in this patient population, but they do have some drawbacks. They have to be administered in a specialized facility and they are associated with fairly high rates of cytokine release syndrome and neurotoxicity.
The rates of grade 3 to 4 cytokine release syndrome and neurotoxicity with glofitamab were low, but not negligible. All cytokine release syndrome events were manageable, and no patients discontinued treatment because of adverse events. This is, potentially, attractive, because it offers an active therapy to a broader subset of patients with MCL who may not be able to access CAR T-cell therapy as easily. A phase 3 trial is in the planning stages, and it is likely that if that trial has positive results, we will see glofitamab approved in the not-too-distant future for people with MCL, and having more options is always great.
Based on these developments, do you see any shifts in your day-to-day practice in the future?
Dr. Martin: I think what has been interesting to me about MCL over the past decade is this idea that not everybody is the same. That should not come as a surprise statement, but MCL does behave differently in different people.
As a physician who treats a lot of patients with MCL, I have seen all of the different ways in which MCL can behave; combine that with the heterogeneity of humanity as a whole. Having guidelines from the NCCN (National Comprehensive Care Network) are helpful, but those guidelines are broad.
Learning how to take all that heterogeneity and variety into account and match the appropriate treatment to each patient is important. What these front-line trials are telling us is that it is OK to do research that does not involve chemotherapy.
In the past, it might have been considered unethical to give a younger patient a treatment without autologous stem cell transplant. But that is clearly not the case now. I think that in real-life practice in the near future, guidelines may actually start to get a little bit easier to follow as we come up with options that are less intensive.
It may be that patients can access treatments that are a little bit easier, that do not involve a transplant. That would be good for people with MCL from all across the country.