Targeting BTK with Ibrutinib in Relapsed or Refractory Mantle-Cell Lymphoma

SUMMARY:The FDA granted accelerated approval to Ibrutinib (IMBRUVICA®), for the treatment of patients with Mantle Cell Lymphoma (MCL), who had received at least one prior therapy. Bruton's Tyrosine Kinase (BTK) is a cytoplasmic protein predominantly expressed in B-cells and is a mediator of B-cell receptor signaling in normal and transformed B-cells. BTK is necessary for the proliferation and survival of B-cell tumors. IMBRUVICA® is an oral, irreversible inhibitor of BTK and thereby inhibits cell proliferation and promotes programmed cell death (Apoptosis). The efficacy of IMBRUVICA® was evaluated in a multi-center, international, single-arm Phase II trial in which 111 patients with previously treated MCL, received IMBRUVICA®, at a daily oral dose of 560 mg. The median age was 68 years and patients had received a median of three prior therapies. Patients were stratified into those who had previously received at least 2 cycles of VELCADE® (Bortezomib) therapy and those who had received less than 2 cycles or had no prior therapy with VELCADE®. More than 80% of patients had intermediate-risk or high-risk disease. Treatment was given until disease progression or until unacceptable toxicities were noted. The primary end point was Overall Response Rate (ORR). Secondary end points included duration of response, Progression Free Survival (PFS), Overall Survival (OS), and safety. With a median follow-up of 15.3 months, the ORR was 68%, with a 21% Complete Response and 47% Partial Response rate. The estimated median duration of response was 17.5 months. Prior treatment with VELCADE® had no influence on the Response Rate (RR). The median PFS was 13.9 months and estimated OS was 58% at 18 months. Treatment related toxicities were mild to moderate nausea, diarrhea, fatigue, and cytopenias. Grade 3 bleeding was noted in 5% of the patients, but these patients had a history of falls and were receiving either Aspirin or Warfarin. The authors concluded that IMBRUVICA® given as a single agent has durable efficacy in relapsed or refractory MCL. Studies are underway, combining IMBRUVICA® with TREANDA® (Bendamustine) and RITUXAN® (Rituximab), as front line therapy for patients with MCL. The list of agents for the treatment of relapsed or refractory MCL now include VELCADE®, REVLIMID® and IMBRUVICA®. Wang ML, Rule S, Martin P, et al. N Engl J Med 2013; 369:507-516