Introduction: Carfilzomib is a next-generation proteasome inhibitor that selectively and irreversibly binds to its target, resulting in sustained inhibition absent of off-target effects relative to bortezomib. Carfilzomib has demonstrated durable anti-tumor activity and an acceptable tolerability profile in patients with multiple myeloma (MM). Final results will be presented for the bortezomib-naïve group of PX-171-004, a phase 2 study of single-agent carfilzomib in patients with relapsed and/or refractory MM. Herein we report the most recent data analysis available at time of abstract submission. Updated final results for the bortezomib-naïve group of PX-171-004, including OS data, will be presented at the meeting.
Methods: Patients received either 20 mg/m2 for all treatment cycles (Cohort 1) or a stepped-up dose-escalating regimen of 20 mg/m2 for Cycle 1 and 27 mg/m2 for all treatment cycles thereafter (Cohort 2). Carfilzomib was administered over 2–10 minutes on Days 1, 2, 8, 9, 15, and 16 of every 28-day cycle, for a maximum of 12 cycles. The primary endpoint was the best overall response rate (ORR; [CR + VGPR + PR]) determined according to the IMWG Uniform Response Criteria. Secondary endpoints included the clinical benefit response rate (CBR; [ORR + MR per EBMT criteria]), progression-free survival (PFS), time to progression (TTP), duration of response (DOR), OS, and safety. The result of efficacy analysis from disease assessment by the Independent Review Committee is presented in this abstract.
Results: 127 of 129 enrolled bortezomib-naïve patients were evaluable for response. Prior therapies included thalidomide (59%), lenalidomide (59%), alkylating agents (81%), and stem cell transplant (73%). Patients had received a median of 2 prior regimens (1 in 54 patients, 2 in 40 patients, 3 in 28 patients, and ≥4 in 7 patients). 84 patients (65%) were disease refractory to their most recent therapy, defined as ≤25% response or progression during or within 60 days after completion of therapy. The median duration of carfilzomib treatment is 7 cycles (range 1−12) in Cohort 1; 8 patients were receiving drug as of February 2011 in Cohort 2 with a median treatment of 6.5 cycles (range 1−13) at that time. Best ORR was 42% in Cohort 1 and 52% in Cohort 2. Median TTP was 8.3 months and median DOR was 13.1 months in Cohort 1. The median TTP and DOR for Cohort 2 have not been reached at the time of this interim analysis; the lower bound of the 95% CI for the median TTP was 10.2 months, and 84% were estimated to have DOR ≥1 year at the time of data cutoff. Higher response rates for Cohort 2 compared with Cohort 1 do not appear to be associated with higher toxicities. Patients with unfavorable cytogenetic characteristics (≥1 abnormality) per mSMART criteria had an ORR of 37% and CBR of 42% compared with 50% and 65%, respectively, for patients with no abnormality. The most common treatment-emergent adverse events (AEs), regardless of relationship to carfilzomib in Cohorts 1 and 2, respectively, were fatigue (71%, 54%), nausea (54%, 43%), anemia (46%, 37%), and dyspnea (49%, 33%). These were primarily ≤Grade 2 in severity. The most common Grade 3/4 AEs were anemia (15%), lymphopenia (15%), thrombocytopenia (13%), pneumonia (12%) and neutropenia (12%). Treatment-emergent peripheral neuropathy (PN) was mild and infrequent (16%). Only 1 case of Grade 3 PN (0.8%) was observed. Overall, 38 patients (30%) completed 12 cycles and 22 of these patients continued to receive carfilzomib therapy under a safety extension protocol (PX-171-010), an ongoing, multicenter, open-label phase 2 study to monitor long-term use of single-agent carfilzomib.
Conclusions: To date we have seen robust and durable single-agent activity for carfilzomib in bortezomib-naïve patients with relapsed and often refractory MM with an ORR of 42−52% and a CBR of 59−63% from 2 separate dose cohorts in a population wherein 92% received an immunomodulatry drug and 73% had undergone an autologous stem cell transplant previously. These data are suggestive of a dose–response relationship and are being further evaluated in the exploratory phase 1b/2 study PX-171-007. Carfilzomib was associated with minimal PN and excellent long-term tolerability, with nearly one-third of patients completing 12 cycles and 22 of these continuing treatment beyond 1 year in the extension protocol PX-171-010.