Ibrutinib Combined With Venetoclax Demonstrates Acceptable Safety in MCL

In this interview, Constantine Tam, MD, Peter MacCallum Cancer, Melbourne, Australia, discusses results from a lead-in safety analysis of ibrutinib in combination with venetoclax for the treatment of patients with mantle cell lymphoma. This combination will be compared with ibrutinib monotherapy in the phase 3 SYMPATICO study.

This interview was modified from an original recording published on Population Health Learning Network.

What existing data led you and your co-investigators to conduct this research?

We know that the two drugs that we combined together in this study, ibrutinib and venetoclax, work individually in the treatment of mantle cell lymphoma, but the responses were incomplete. With either ibrutinib or venetoclax, we expect about a 20% complete remission rate. We hypothesized that, when you combine the two drugs together, that you might get a higher response rate.

Indeed, we have previously shown in a smaller phase 2 study ran by my institution that combining the two drugs together results in a complete remission rate of 71%, and seems to improve outcomes, especially for patients with poor prognosis mantle cell lymphoma, like those with p53 mutations.

The current study is an extension of our previous work. What we have done is we have taken the single institutional study to a multinational study. Also, we have modified the schedule so that the two drugs, ibrutinib and venetoclax, are started at the same time to try and prevent those patients who have caught early drug failure.

In our previous study, we started with ibrutinib for one month to debulk prior to venetoclax, and that reduced the risk of tumor lysis syndrome, but the price that we pay was that some patients progressed through the first month of ibrutinib.

In the current study, what we have done is we are exploring the safety of starting the two drugs together at the same time.

Please briefly describe your study and its findings. Were any of the outcomes particularly surpising?

The current study is actually the safety running phase for a phase 3 study, which then the phase 3 study is comparing ibrutinib and venetoclax against ibrutinib monotherapy in patients with mantle cell lymphoma.

We did a safety running to explore the feasibility of giving the two drugs simultaneously from day one, and we enrolled 21 patients, of which 15 were high-risk for tumor lysis, 6 were low-risk for tumor lysis.

All those patients started with both ibrutinib and venetoclax from day one, with the obvious concern is whether they will observe tumor lysis when you start both drugs at the same time.

What is surprising, and it's pleasantly surprising, is that there were actually very few tumor lysis events. In fact, of the 21 patients, only one patient who is a high-risk patient developed laboratory tumor lysis syndrome, and no patient developed clinical tumor lysis syndrome.

The conclusion from that is that it is quite safe. It is safe to start the two drugs together, which is what we did in the phase 3 portion of the study, comparing the combination vs ibrutinib monotherapy, but the results of the phase 3 study are not yet reported. We are only reporting the safety running portion.

Are there any real-world applications of these findings in clinical practice?

At the moment, everything we have is investigational. The combination of ibrutinib and venetoclax has not been proven in a randomized setting to be better than ibrutinib, even though the response rate and everything looks very promising.

I will say that it will not be regarded as standard of care to use the combination therapy. I think that what this will obviously lead to, once we show that the combination is hopefully better than monotherapy, is that this would lead to widespread adoption of ibrutinib and venetoclax as second-line therapy for patients with mantle cell lymphoma, instead of ibrutinib, which is currently the standard second-line therapy.

What hopefully our work also show is that it is possible to start the two drugs simultaneously, which will simplify the schedule and minimize the risk of tumor breakthrough on the first month of ibrutinib monotherapy.

Do you and your coinvestigators intend to expand upon this research?

At the moment, obviously, the phase 3 study needs to be finished to hopefully show that there is a benefit to the combination. Then, really, the area that I see as most needed is identifying those patients who do not respond to the combination.

Maybe about one in five patients, despite this really potent, nice combination, do not have a response. At the moment, we're only starting to understand the genetics of why that happens. Hopefully, with more experience, we can identify those patients who are likely to not respond to directing the alternative therapy, and work out ways to overcome that resistance.

Is there anything else you would like to add?

Although safety was the primary end point of the current report, we also looked at efficacy. In the 21 patients, the efficacy was actually reassuringly good. The overall response rate was 81%, the complete remission rate was 62%, and at 18 months, the progression-free survival was 75%.

These are all really better than expected for either ibrutinib or venetoclax monotherapy, and in line with our previous smaller phase 2 experience in our institution, where we had, once again, a high response rate and durable progression-free survival. This is a validation of the data that we have previously seen.