GLASGOW – Patients with relapsed or refractory mantle cell lymphoma (MCL) who experience disease progression on a Bruton’s tyrosine kinase inhibitor (BTKi) may respond best to a combination of rituximab, bendamustine, and cytarabine (R-BAC), based on early results from an ongoing retrospective study.
Findings from the study, which were presented at the annual meeting of the British Society for Haematology, showed that R-BAC after BTKi failure had an overall response rate (ORR) of 90.5%.
This is a “remarkable response rate” according to the investigators, who cited previously reported response rates for other treatments ranging from 29% to 53%.
Treatment of relapsed/refractory MCL patients in the post-BTKi setting is an area of unmet clinical need, said senior author, of the University of Plymouth, England. He noted that there is currently no consensus regarding best treatment strategy for this patient population.
Dr. Rule said that he and his colleagues have collected data on 30 patients so far, of which 22 were included in this early data release.
All patients received R-BAC between 2016 and 2018 at treatment centers in Italy and the United Kingdom. Treatment consisted of rituximab (375 mg/m2 or 500 mg) on day 1, bendamustine 70 mg/m2 on days 1 and 2, and cytarabine 500 mg/m2 on days 1 through 3, given in a 28-day cycle.
Patients received R-BAC immediately after BTKi failure. Data were drawn from hospital records.
Analysis showed that the median patient age was 65 years, with a range from 43 to 79 years. Most patients were men (81.8%), 55.0% were high risk based on the Mantle Cell Lymphoma International Prognostic Index, and 22.7% had blastoid morphology.
Patients had a median of two prior systemic therapies, with a range from one to six lines. First-line therapies included rituximab in combination with HDAC (high-dose cytarabine containing regimen), CHOP, CVP, or ibrutinib. Nine patients (42.9%) had allogeneic stem cell transplantation (ASCT) after induction treatment.
For BTKi therapy, most patients received ibrutinib (n = 18), while the remainder received acalabrutinib, tirabrutinib or M7583. Most patients discontinued BTKi therapy because of disease progression (90.9%); two patients stopped because of a lack of response (9.1%).
The median number of R-BAC cycles received was four. Two patients started with attenuated doses and seven patients reduced doses after the first cycle. More than 70% of patients completed R-BAC treatment.
The estimated median progression-free survival was 7.3 months and estimated median overall survival was 11.2 months.
Although the investigators reported a complete response rate of 57.1%, they noted that this figure “may be exaggerated” because of a lack of bone marrow biopsy; however, they suggested that the overall response rate (90.5%) “should be accurate.”
During the course of treatment, 31.8% of patients required inpatient admission, 22.7% developed neutropenic fever, and 77.8% required transfusion support. No treatment-related deaths occurred.
“This population, enriched for patients with high risk features, showed remarkable response rates to R-BAC,” the investigators wrote. “The treatment had acceptable toxicity, maintained efficacy at attenuated doses, and was used successfully as a bridge to ASCT in over 20% of patients.”
The investigators suggested that R-BAC should be considered a new standard of care in the United Kingdom for bendamustine-naive patients who are unable to be enrolled in clinical trials. “The high response rate makes it particularly appealing for patients considered candidates for consolidation ASCT,” they wrote.
In an interview, Dr. Rule added perspective to these findings.
“There’s been an obsession with venetoclax, that that’s the answer, but it really isn’t,” Dr. Rule said. “So people are looking for a new drug. I guess what I do differently to most people is I use CHOP frontline rather than bendamustine. To me, that’s the best way of sequencing the therapies, whereas if you use [bendamustine and rituximab] up front, which a lot of people do, particularly in the [United] States, your R-BAC might not be so effective.”
However, Dr. Rule said that first-line therapies appear to have minimal impact on R-BAC efficacy. “Even if you’ve had bendamustine, even if you’ve had high-dose cytarabine, even if you’ve had an allogeneic stem cell transplant, [R-BAC] still works,” he said.
Where patients have issues with tolerability, Dr. Rule noted that dose reductions are possible without sacrificing efficacy.
He offered an example of such a scenario. “My oldest patient was about 80 with blastoid disease, relapsing,” Dr. Rule said. “After ibrutinib, I gave him just a single dose of bendamustine at 70 mg, a single dose of cytarabine at 500 mg, just 1 day, and he had that six times, probably 3 weeks apart. He’s been in complete remission for over a year.”
With data on 30 patients collected, Dr. Rule said that he and his colleagues plan to present more extensive findings at the European Hematology Association Congress, held June 13-16 in Amsterdam.
The investigators reported having no conflicts of interest.