NEW YORK—Despite an “unprecedented” single-agent response rate and progression-free survival (PFS) in previously treated mantle cell lymphoma (MCL) patients, those with multiple risk factors have a dismal outcome following ibrutinib failure.
So after ibrutinib, what’s next in MCL? That was the question asked at Lymphoma & Myeloma 2015.
Peter Martin, MD, of Weill Cornell Medical College in New York, New York, discussed some possibilities.
Ibrutinib (Imbruvica) was approved by the US Food and Drug Administration for MCL based on the PCYC-1104 trial, which showed an overall response rate of 68%. In the MCL2001 trial, the overall response rate was 63%.
The median PFS for MCL was 13 months in PCYC-1104 and 10.5 months in MCL2001. The median overall survival (OS) was close to 2 years in PCYC-1104 and 18 months in MCL2001.
“So this is where I think it starts to get interesting,” Dr Martin said. “People were able to live for several months after progressing on ibrutinib. [However,] our experience at Cornell was not necessarily consistent with that.”
Cornell investigators, along with colleagues from Ohio State University, compiled data on patients who had been treated in clinical trials at their institutions and reviewed their survival after progression on ibrutinib. These patients had a median OS of 4 months.
In reviewing the patients’ Mantle Cell Lymphoma International Prognostic Index (MIPI) scores, Dr Martin said they were arguably a higher-risk population.
Dr Martin collected data on 114 relapsed/refractory MCL patients from centers around the world and found they had a lower response rate (50%) with ibrutinib overall and a lower duration of ibrutinib therapy (4.7 months).
The median OS after stopping ibrutinib was 2.9 months for the entire group. For patients who did not receive any subsequent therapy after failure, it was 0.8 months. Patients who received treatment after ibrutinib failure had a median OS of 5.8 months.
“And it didn’t seem to matter what we gave,” Dr Martin said. “Those treatments were pretty short-lived.”
The median time to next treatment with the first subsequent therapy was 2.4 months. These therapies included bendamustine, cytarabine, and lenalidomide.
“There was no statistical association between survival and choice of therapy,” Dr Martin said.
What was significant, by univariate Cox regression analysis, was the patients’ MIPI prior to ibrutinib therapy (P=0.0002) and the duration of ibrutinib treatment (P=0.0465).
“So at this point in time, I think it’s fair to say that there is insufficient data to recommend any specific treatment following ibrutinib failure,” Dr Martin said.
However, he did make a few suggestions for treating high-risk patients.
Treatment suggestions after ibrutinib failure
Dr Martin’s first suggestion is to focus on symptom management rather than active therapy for the older, frailer patients. Second, consider allogeneic stem cell transplant in any high-risk patient responding to ibrutinib.
Third, consider continuing ibrutinib therapy while starting the next therapy. And fourth, consider some form of continuous therapy that does not depend on TP53.
Dr Martin admitted that what to do following ibrutinib failure remains cloudy.
“Conducting a clinical trial will be tricky,” he said, “because the median time from ibrutinib failure to the next therapy was 9 days, and we’re targeting a very high-risk patient population.”
In addition, on average 80% have expression of Ki67.
Currently, a phase 2 trial of copanlisib (NCT02455297) is the only post-ibrutinib clinical trial in MCL open. Copanlisib is a potent and reversible phosphatidylinositol-3-kinase (PI3K) inhibitor with activity against both alpha and delta isoforms of PI3K. Preliminary results of the trial demonstrated response in 5 of 7 MCL patients.
So perhaps the best approach, Dr Martin suggested, would be to improve response and prevent relapse while on ibrutinib using combination therapies.
A phase 1/1b trial of ibrutinib with bendamustine and rituximab (BR) is underway. Of 17 MCL patients treated thus far, 94% have responded, and 76% have achieved a CR. But 25% developed grade 3 rash.
Ibrutinib is also being studied in combination with rituximab in MCL. The combination has produced an overall response rate of 88%, with 40% of patients achieving a CR.
“My interpretation from all these studies is you can probably add ibrutinib to any other effective anti-MCL therapy and improve that therapy,” Dr Martin said. “But there are questions, obviously, that still arise.”
Overcoming ibrutinib resistance
Dr Martin explained that, to use combinations rationally, we need to understand mechanisms of ibrutinib resistance, “and that’s not so straightforward.”
Mutations in MCL likely have multiple mechanisms of resistance. Mutations occur predominantly in 3 groups of genes involving NF-kB, PIM/mTOR, and epigenetic modifiers.
A number of trials are underway to hit some of these pathways, Dr Martin said.
Researchers at Cornell are studying ibrutinib plus palbociclib, an inhibitor of CDK4/CDK6 approved for advanced breast cancer, in a phase 1 trial of MCL patients.
The combination “very early on, has seen a high number of complete responses, which have been exciting,” Dr Martin said.
There are many ongoing ibrutinib trials in previously treated patients, including ones with carfilzomib, palbociclib, bortezomib, venetoclax, lenalidomide, and TGR-1202. In addition, the frontline trial of BR +/- ibrutinib is expected to have results soon.
“[A]nd once that happens, my guess is that this frontline trial, once it’s read out, essentially, makes all these other trials irrelevant because the minute ibrutinib moves into the frontline setting, it makes it very difficult to evaluate in a subsequent setting,” Dr Martin said. “So within a couple of years, it will be standard in the frontline setting.”
Dr Martin is concerned that resources are insufficient—there are too many studies, too few patients, and too little time—to find another, potentially more effective agent or combination.
He said there won’t be a one-size-fits-all approach to MCL either before or after ibrutinib, and collaboration among institutions, companies, and cooperative groups will be needed.
“Management in the post-ibrutinib setting remains unclear,” he said, “and these patients should be treated in a clinical trial if possible.”