In some lymphomas, ibrutinib yields “almost unheard-of” survival rates

Younger patients with two genetic subtypes of diffuse large B cell lymphoma (DLBCL) – specifically MCD and N1 – show substantial improvements in survival with the addition of ibrutinib to standard R-CHOP chemotherapy, compared with R-CHOP alone, new research shows.

The findings, published Nov. 4, 2021, in Cancer Cell, come from a subanalysis of the phase 3 Phoenix trial. They show that patients with DLBCL aged 60 and younger with either the MCD or N1 genetic subtype had 3-year event-free survival rates as high as 100% when treated with ibrutinib plus R-CHOP, whereas with R-CHOP chemotherapy alone, the survival rates were approximately half of that rate.

“A 100% 3-year event-free survival is almost unheard-of in DLBCL and speaks to the intense dependency of these subtypes to constitutive B cell receptor signaling and their vulnerability to ibrutinib,” first author Louis M. Staudt, MD, of the Lymphoid Malignancies Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Md., said in an interview.

“By contrast, in ABC DLBCL, the addition of ibrutinib to R-CHOP increased event-free survival by 12.4% to 76.9% in younger patients,” Dr. Staudt said.

ABC, along with GCB and unclassified, are among three key genetic classifications of DLBCL, which is the most common type of lymphoma. While previous studies have shown the Bruton kinase (BTK) inhibitor ibrutinib to induce very low responses among those with the GCB type, favorable responses are seen with the ABC type, of which MCD and N1 are genetic subtypes.

For the Phoenix trial, 838 previously untreated DLBCL patients of the ABC subtype were randomized to ibrutinib (560 mg per day, orally) or placebo plus R-CHOP, in a 21-day cycle for 6 or 8 cycles.

In the overall population, the study failed to achieve its primary survival endpoint of improved survival with ibrutinib. However, a subset analysis stratifying patients by age revealed significant event-free, progression-free, and overall survival benefits with ibrutinib among patients aged 60 and under, with manageable safety. Unexpectedly, this treatment was associated with a worsening of survival outcomes among patients over 60, due to toxicities.

In the new subanalysis, focusing on patients aged 60 and under, Dr. Staudt and his colleagues found that those with the MCD subtype of ABC DLBCL (n = 31) who were treated with ibrutinib had 3-year event-free survival and overall survival rates as high as 100% each, while these rates were significantly lower with R-CHOP alone (48%; P = .01, and 69.6%; P = .032, respectively).

Likewise, among younger patients with the N1 subtype (n = 13), the addition of ibrutinib was associated 3-year event-free and overall survival of 100%, while the R-CHOP alone patients had a significantly lower event-free- (50%; P = .0161) and overall survival (50%; P = .0134).

In the study in general, younger patients who were neither MCD nor N1 also showed better responses with ibrutinib versus placebo; however, the effects were not as strong as those with the MCD and N1 genetic subtypes.

Older patients over 60 showed no benefit from ibrutinib, regardless of their genetic subtype. And benefits were not observed in younger patients with BN2 DLBCL (n = 21), another ABC subtype.

The results are important – despite being secondary endpoints, Dr. Staudt emphasized.

“The automatic assumption regarding secondary endpoints is that any positive findings might have occurred by chance. In the present study, we show that this is not the case.”

“Rather, two previously defined genetic subtypes of DLBCL had an exceptional benefit from ibrutinib,” he said.

“Our study provides strong biological support for the view that the original Phoenix trial should be viewed as a positive trial for younger patients (under 60) with non-GCB DLBCL,” Dr. Staudt said.

While the responses to ibrutinib among younger ABC patients in general were not as robust as with the MCD and N1 subtypes, those improvements nevertheless suggest important benefit with the added treatment, he noted.

“Overall, MCD and N1 constitute roughly 10% of DLBCLs; however, our conclusion is that ibrutinib should be considered in younger patients with non-GCB DLBCL, which constitutes roughly 43% of all DLBCLs,” he said.

Dr. Staudt and other authors are inventors on NIH patent applications covering the LymphGen algorithm (a genetic predictor tool) and covering the use of BTK inhibitors in genetic subtypes of DLBCL. The Phoenix trial received support from Janssen Global Services.

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