Does Acalabrutinib Fit Into Frontline MCL Therapy?

For younger, fit patients with mantle cell lymphoma (MCL), adding the Bruton’s tyrosine kinase (BTK) inhibitor acalabrutinib to standard induction therapy with bendamustine/rituximab followed by cytarabine/rituximab adds toxicity without improving efficacy, results of the phase 2 ECOG-ACRIN EA4181 trial indicate. 

However, treating patients with bendamustine/rituximab plus acalabrutinib might be preferred to either option with cytarabine.

Although the results showed that the bendamustine/rituximab plus acalabrutinib regimen was not superior to standard induction therapy with or without acalabrutinib, it was the least toxic option. 

Standard induction therapy can be still be considered the standard for this patient population, but eliminating cytarabine represents “an appealing option to avoid high-dose cytarabine,” said study investigator Nina Wagner-Johnston, MD, from Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins Hospital, Baltimore, during a presentation of the findings at the American Society of Hematology 2024 annual meeting. 

The bendamustine/rituximab plus acalabrutinib regimen, where acalabrutinib replaced high-dose cytarabine, is “the most intriguing arm of the study,” Marcus Messmer, MD, with the Department of Hematology/Oncology, Fox Chase Cancer Center, Philadelphia, told Medscape Medical News. 

“The results suggest that bendamustine/rituximab plus acalabrutinib may be equivalent in efficacy to [standard induction] with less toxicity,” said Messmer, who was not involved in the study. 

Unfortunately, the study was not designed to show non-inferiority of bendamustine/rituximab plus acalabrutinib compared to standard induction therapy, and the bendamustine/rituximab plus acalabrutinib arm was stopped early due to a lack of a superiority signal, Messmer added.

Inside the Findings

MCL is a rare and aggressive B-cell lymphoma that poses unique treatment challenges, particularly in younger patients, for whom the treatment “landscape is shifting rapidly,” Wagner-Johnston explained.

Wagner-Johnston noted that the optimal induction regimen for fit, younger patients with MCL is unclear, although the mainstay of treatment is intensive chemoimmunotherapy with cytarabine.

The standard bendamustine/rituximab followed by cytarabine/rituximab induction regimen is associated with high complete remission and undetectable measurable residual disease, with evidence of improved progression-free survival, she noted. 

“And we know that BTK inhibitors, in combination with chemoimmunotherapy, are highly effective in MCL and that achieving molecular remission or undetectable measurable residual disease is an independent predictor of long-term outcomes in patients. All of these features were key when designing ECOG-ACRIN EA 4181,” Wagner-Johnston told attendees. 

The study enrolled 369 patients, 18-70 years old, with untreated MCL, ECOG performance score 0-2, and adequate organ and marrow function. Study participants were randomized 1:1:1 to the standard induction control arm or to one of two experimental arms. These included the control arm of induction therapy with three cycles of bendamustine/rituximab followed by three cycles of cytarabine/rituximab, the standard induction plus acalabrutinib across both cycles, or six cycles of bendamustine/rituximab with acalabrutinib.

In the standard induction plus acalabrutinib arm, acalabrutinib was dosed continuously at 100 mg twice daily during the initial cycles, and during weeks 1 and 3 of the latter cycles.

The primary analysis focused on 260 patients with an end-of-treatment sample sent for measurable residual disease testing. Roughly 90% of patients completed study treatment, with no differences between treatment arms. 

The primary outcome was a composite of PET/CT complete molecular remission and peripheral blood undetectable measurable residual disease. In the control arm, 82% of patients achieved the primary outcome, as did 82% of patients in the standard induction plus acalabrutinib arm and 78% in the bendamustine/rituximab plus acalabrutinib arm. 

“Notably, neither of the experimental arms were superior to the standard-of-care arm across the board,” Wagner-Johnston said. Overall response rates were “quite high,” with complete response rates of more than 90%, with no differences between the arms, she noted. 

Similarly, no significant difference was seen in progression-free survival or overall survival between treatment arms. At a medium follow up of roughly 28 months, the 12-month progression-free survival rate was 90%-92% across the three groups.

The team also evaluated progression-free survival by measurable residual disease status, regardless of whether patients completed protocol therapy. “Not surprisingly,” said Wagner-Johnston, progression-free survival was superior for those with undetectable measurable residual disease compared with those with detectable levels — but again there was no differences between treatment arms. 

Grades 3-5 treatment-related adverse events occurred in at least 5% of patients and were mostly hematologic. 

The bendamustine/rituximab plus acalabrutinib was associated with significantly less hematologic toxicity, with a febrile neutropenia rate of 4.0% vs 8.9% in the standard induction arm and 9.3% in the standard induction plus acalabrutinib arm. 

Grades 3-5 treatment-related anemia rates were much lower in the bendamustine/rituximab plus acalabrutinib arm (3.0% vs 18.5% for standard induction and 24.8% for standard plus cytarabine). Similarly, the bendamustine/rituximab plus acalabrutinib arm had lower rates of treatment-related grade 3 or higher thrombocytopenia (6.0% vs 44.4% and 51.2%, respectively). 

Across all three treatment groups, rates of neurotoxicity, renal toxicity, bleeding/hemorrhage, and cardiac toxicity were low.

Treatment discontinuations due to adverse events were also low (7%) across the arms, with five treatment-related deaths reported. 

“Standard high-dose cytarabine requires inpatient administration and carries risk of neurologic and hematologic toxicity, making it particularly difficult to give in a community setting,” Marcus told Medscape Medical News. “This study, along with updated results from the TRIANGLE study, suggests that we are moving away from high-dose cytotoxic therapy and toward targeted therapy in frontline management of mantle cell lymphoma.”

The study was supported by the National Cancer Institute. Wagner-Johnston has received research founding from Genentech, Merck, and AstraZenecca and consults for Beigene. Marcus had no relevant disclosures.