Long-Term Safety and Efficacy of Orelabrutinib Monotherapy in Chinese Patients with Relapsed or Refractory Mantle Cell Lymphoma: A Multicenter, Open-Label, Phase II Study

Background: In spite of years of effort, Mantle Cell Lymphoma (MCL) remains a clinical challenge. The clinical significance of Bruton's Tyrosine Kinase (BTK) inhibitor has been validated with the approvals by FDA for the treatment of multiple subtypes of NHL including refractory and relapse (r/r) MCL. However, some serious adverse events (AEs) due to poor target selectivity (inhibition of EGFR, TEC, BMX and others), such as diarrhea, sever bleeding and atrial fibrillation, remain as challenges in clinic. Orelabrutinib is a novel, potent irreversible BTK inhibitor with high selectivity for BTK. Results of early clinical study showed that it has excellent safety/tolerability profiles and favorable pharmacokinetic/pharmacodynamic properties. Sustained ~100% BTK occupancy at 24 hours was achieved with once daily dosing regimen of 50 mg and above. In this presentation, we will report an updated analysis of orelabrutinib in Chinese patients with r/r MCL with minimum of 12 cycles of treatment.

Aims: To evaluate the sustained efficacy and long-term safety of orelabrutinib in Chinese patients with r/r MCL.

Methods: This is an open-label, multicenter, two stages, phase II study. The primary endpoint was objective response rate (ORR) assessed per Lugano criteria (2014). Safety and other efficacy (DOR, PFS, OS) evaluations were chosen as secondary endpoints.

Results: A Total 106 patients, were enrolled in this study with median follow up time of 15.0 months. 79.2% of the patients were male and median age of 62.0 years old. Most patients were at advanced stage (73.6% were at stage IV and 20.8% were at stage III). According to per protocol analysis, 87 (87.9%) patients achieved ORR and 93.9% patients achieved disease control. The median duration of response (DOR) was not reached, the DOR rate at 12 months was 73.7%, as expected the median PFS and OS were not reached, the PFS and OS rates at 12-month were 70.8% and 88.7% respectively. Comparing to the results of previous analysis, the CR rate, by conventional CT method, increased to 27.4% and it was expected a higher rate of in depth response may occur with prolonged treatment. Further analysis showed orelabrutinib was efficacious in all subgroups (age, gender, status, stage, prior therapy, etc.). Orelabrutinib demonstrated excellent safety profile in r/r MCL patients. The frequently reported treatment related adverse events (TRAE) were primarily hematological toxicities including thrombocytopenia, neutropenia, leukopenia, and hypertension. The frequently reported grade 3 or higher AEs of any cause was thrombocytopenia . No treatment related ≥grade 3 GI and cardio toxicity, nor severe bleeding, were observed. Of the 106 patients, 32 experienced serious AEs; and 17 of them, mainly hematological toxicities and / or infections were treatment-related. Comparing to the safety data of median follow up of 10.5 months, there was only a mild increase of adverse events rate after extended treatments; the safety profiles were essentially the same. These results suggested that safety events primarily occurred during early treatment and it appeared less eventful with orelabrutinib continue treatment.

Conclusion: Orelabrutinib showed continuous efficacious in treating patients with r/r MCL. In addition, orelabrutinib is safe and well tolerated with no treatment related grade 3 or higher diarrhea, atrial fibrillation/flutter or severe bleeding in this study. Results of prolong treatment expected to produce a higher rate of in depth response without altering its safety profiles support orelabrutinib being a better selection for BTKi therapy. The improved safety as a resulting of high target selectivity, and the convenience of daily dosing regimen provides orelabrutinib as preferred therapeutic choice for B cell malignancy.