High-Dose Carfilzomib and Dexamethasone As First-Line Treatment in Symptomatic Multiple Myeloma

Background: Carfilzomib (Cfz) is approved for use in relapsed and refractory multiple myeloma (RRMM) at a dose of 27mg/m2 after escalation from 20mg/m2. The response rate for Cfz and dexamethasone (dex) as first-line therapy in multiple myeloma (MM) is unknown. Higher doses of Cfz have been shown to enhance overall response in RRMM (Lendvai 2014); the presence of a dose-response relationship of Cfz for first-line therapy in untreated MM has not been evaluated. A protocol of Cfz-Dex induction at two dosing levels, followed by BiRd (Clarithromycin 500mg PO BID, Lenalidomide (Len) 25mg for 21/28 days, Dex 40mg weekly) consolidation, and thereafter Len (10mg 12/28 days) maintenance, evaluated response and safety by Cfz dose level in patients (pts) with newly diagnosed symptomatic MM. The ORR and safety data for Cfz-Dex induction stratified by Cfz dose is reported.

Methods: 70 patients with untreated MM were enrolled in a phase 2 study of Cfz-dex. Cfz-dex is: Cfz IV on D1, 2, 8, 9, 15, 16 of a 28-day cycle at a dose of 20mg/m2 on days 1, 2 of cycle 1 and 45mg/m2 thereafter and Dex 40mg on D1, 8, 15, 22. After the first 26 pts were enrolled, the protocol was amended to increase the Cfz from 45 to 56mg/m2. Screening echocardiogram and pulmonary function testing were performed. Brain natriuretic peptide (BNP) was measured with each cycle. Cfz-dex was continued until plateau in disease response (unchanged M-protein for 2 cycles). Elective stem cell collection was then performed in transplant eligible pts. This was followed by BiRd until 2^nd response plateau, and then by LEN maintenance. Disease response evaluation was performed monthly with serum and urine protein electrophoresis, immunofixation, and free light chain analysis; bone marrow biopsy with skeletal imaging was used to confirm MM progression or complete response (CR). Cytogenetic testing was performed on CD138-selected cells.

Results: 25 pts received Cfz-Dex at 45 mg/m2 and 44 (out of 45 enrolled) pts at 56 mg/m2 for at least 1 cycle and were evaluable for response. 56% of pts were ISS II/III and 64% had high-risk cytogenetics as per IMWG definition. Pts received a median of 5 cycles of Cfz-dex in both the 45 mg/m2 (range 1-10) and 56 mg/m2 groups (range 1-14). Maximum response to Cfz-dex is shown in Table 1. There was no difference in response between the 45 and 56mg/m2 groups (P = 0.20). Median time to PR and maximum response for the 45 and 56 mg/m2 cohorts were both 2 and 3 cycles, respectively. 42 pts had stem cell harvest. All collected stem cells to support at least two transplants (> 5 x 10^6 CD34/kg) in one mobilization attempt using G-CSF, with mean yield of 13.74x10^6 CD34/kg (range 5.94-32.14). 79% collected in 1 apheresis session. Adverse events (AEs) were notable for renal failure in 3 pts (2 Grade 2, 1 grade 3) and congestive heart failure in 1 pt (grade 3). Two of the 3 cases of renal failure occurred in the 56 mg/m2 cohort, all other AEs occurred in the 45mg/m2 cohort. All AEs resolved after stopping Cfz. There was no correlation with TTE, PFTs or serial BNPs and development of cardiac or pulmonary toxicity.

Discussion: This is the first prospective study evaluating induction responses to Cfz-dex in MM. Cfz-dex is safe and active in induction at both 45 and 56 mg/m2, with an ORR of 93% and rate of >= VGPR of 68% despite a primarily high risk population. Specific dose did not correlate with response. Higher dose of Cfz did not lead to more toxicity. Cfz-dex induction led to successful stem cell collection in all attempts. Cfz-dex is a highly active and well-tolerated induction regimen. Transitioning to IMiD-based therapy after maximum response led to deeper responses with a remarkable 97% rate of VGPR or better.