Response Adaptive Salvage Treatment with Carfilzomib-Thalidomide-Dexamethasone for Newly Diagnosed Transplant Eligible Multiple Myeloma Patients Failing Front-Line Bortezomib-Based Induction Therapy - Final Analysis from the Australasian Leukemia and Lymphoma Group (ALLG) MM17 Trial

BACKGROUND

Survival rates in multiple myeloma (MM) have significantly improved in recent decades with the advent of high-dose chemotherapy conditioned autologous stem cell transplantation (ASCT) and the availability of novel agents for induction therapy (Kumar SK et al. Blood 2008). Failure to respond to front-line bortezomib-based induction therapy remains a significant clinical challenge in transplant eligible (TE) newly diagnosed multiple myeloma (NDMM), and is associated with poor outcomes with shortened progression free survival (PFS) and overall survival (OS) (Lee SE et al. Ann Hematol. 2014). In combination with immunomodulatory agents (IMiDs), carfilzomib, a second generation proteosome inhibitor, has been shown to be highly effective in the context of MM induction with high rates of negativity for minimal residual disease (MRD) and few dose limiting toxicities (Langren O et al. Leukemia 2019). The ALLG MM17 trial is a multicentre single arm study of carfilzomib-thalidomide-dexamethasone (KTd) in TE NDMM patients refractory or with suboptimal response to bortezomib-based induction therapy, designed to evaluate the efficacy of early response adaption with a switch to an intensive salvage strategy.

METHOD

Eligible patients included those with TE NDMM, aged 18 years and older, demonstrating sub-optimal response to bortezomib-based induction therapy (failure to achieve a minimal response after 2 cycles, partial response [PR] after 4 cycles, or disease progression within 60 days of completing induction). Salvage therapy consisted of 100mg daily oral thalidomide, with 20 mg of oral dexamethasone and 20mg/56mg of IV carfilzomib on days 1, 2, 8, 9, 15, and 16, with of each 28-day cycle. Following 4 cycles, patients in stringent complete response (sCR) proceeded to melphalan conditioned ASCT whereas those in less than sCR received a further 2 cycles of KTd prior to ASCT. Consolidation therapy consisted of a further 2 cycles of KTd, followed by maintenance 100mg daily thalidomide and 40mg weekly dexamethasone (Td) continuing until progressive disease, unacceptable toxicity, or 12 months of therapy.

Primary objectives were to determine the overall response rate (ORR) and safety profile of treatment with KTd salvage therapy, with secondary objectives to determine the maximal depth of response, progression free survival (PFS), and overall survival (OS) achieved with sequential treatment with KTd salvage, ASCT, post-ASCT consolidation, and maintenance Td therapy. Efficacy assessments were performed via serum protein electrophoresis, serum free light chain and bone marrow evaluation. Next generation flow (NGF) cytometry MRD evaluation of bone marrow aspirate was undertaken pre-ASCT, at day 100 post-ASCT, after 2 cycles of consolidation KTd, and following completion of Td using standardized 8-colour EuroFlow platform.

RESULTS

50 patients were recruited across 6 Australian sites between September 2016 and April 2018. Overall response rate to KTd salvage was 78% (Credible Interval 95%: 64.4-87.1%), with dual proof of concept criteria met (observed ORR ≥ 50% and posterior probability that the true ORR exceeds 30% is ≥ 0.90). Response rates included 12% sCR, 6% CR, 38% VGPR, and 22% PR. Sixteen patients discontinued treatment (32%) including 10 cases (20%) of progressive disease, and 2 patient deaths without progression. NGF MRD negativity was found to be 32%, 36% and 55% at the pre-ASCT, post-ASCT and post-consolidation time-points. At the cut-off date, estimated median follow-up for disease status was 38.6 months and median PFS and OS had not been reached. At 36 months PFS and OS were 63.9% (95%CI: 49.0 - 75.5%) and 79.9% (95%CI: 65.8 - 88.6%) respectively (Figure 1). KTd was found to be well tolerated with 44% of patients experiencing a grade 3 of higher adverse event (AE). Most common AEs included upper respiratory infection (48%), peripheral neuropathy (36%), musculoskeletal pain (32%), dyspnoea (28%), fatigue or lethargy (28%), and constipation (28%). Significant cardiac toxicity was not observed at this higher dose level of carfilzomib.

CONCLUSION

Results demonstrate that response-adaptive utilisation of KTd salvage, ASCT, and consolidation therapy induces high response rates, improving depth of response with high levels of sequential MRD negativity, and durable responses with an acceptable toxicity profile in TE NDMM patients failing bortezomib-based induction therapy.

Figure 1

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Figure 1

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