Consolidation with Carfilzomib, Lenalidomide and Dexamethasone (KRd) Following ASCT Results in High Rates of Minimal Residual Disease Negativity and Improves Bone Metabolism, in the Absence of Bisphosphonates, Among Newly Diagnosed Patients with Multiple Myeloma

Consolidation therapy post autologous stem cell transplantation (ASCT) in patients (pts) with multiple myeloma (MM) seems to deepen disease responses. MRD negativity represents a strong prognostic factor for prolonged remission. Carfilzomib is a second-generation proteasome inhibitor, which in combination with lenalidomide has been associated with high rates of deep responses before ASCT in phase 2 studies. In this context, we prospectively evaluated the role of carfilzomib, lenalidomide and dexamethasone (KRd) as consolidation therapy post-ASCT in newly diagnosed MM pts who have not achieved MRD negative complete remission (CR). The primary endpoint was to assess KRd efficacy in terms of improving disease response, whereas secondary endpoints included percentage of minimal residual disease (MRD) (performed by Next Generation Flow Cytometry) negativity post KRd, safety, time to progression (TTP), time to next treatment (TtNT), overall survival (OS) and the effects of KRd on bone metabolism in the absence of bisphosphonate administration.

All pts achieving at least partial response and less than MRD negativity post-ASCT were eligible for inclusion in the study. Consolidation consisted of 4 cycles of KRd, starting on day 100 post-ASCT: carfilzomib was given at a dose of 20 mg/m² iv on day 1 cycle 1 and 56 mg/m², on days 1, 8, 15 thereafter; lenalidomide was given at 25 mg daily on days 1-21 and dexamethasone at 40mg weekly every 28-days. All pts continued lenalidomide maintenance 10 mg following consolidation until progressive disease. Pts did not receive bisphosphonates during or post-ASCT as well as throughout the period of KRd consolidation. Bone remodeling was evaluated by the following serum indices before and after KRd (2 measurements for each pt): i) osteoclast regulators (soluble receptor activator of nuclear factor kappaB ligand and osteoprotegerin), ii) osteoblast inhibitors (dickkopf-1 and sclerostin) iii) bone resorption markers (CTX and TRACP-5b) and iv) bone formation markers (bone-specific alkaline phosphatase and osteocalcin).

Between January 2018 and May 2019, 39 consecutive pts all MRD positive (20M/19F, median age 56 years, range 44-67 years) entered the study. The distribution per revised ISS was 36.1% stage 1, 52.8% stage 2 and 11.1% respectively. After a median follow-up of 16 months (range 1-17) following KRd initiation, 35 (89.7%) pts had received 4 cycles of KRD, whereas two pts continue on treatment and two discontinued treatment due to toxicity. Following ASCT, one (2.6%) pt had achieved stringent CR (sCR), 4 (10.3%) were in CR, 29 (74.4%) were in very good partial remission (VGPR) and 5 pts (12.8%) were in PR. Post KRd consolidation, 30 out of 37 evaluable pts (81%) pts improved their response status with KRd. Overall, 28 (75.7%) pts achieved a sCR, one (2.7%) CR and 8 (21.6%) VGPR, while 25 (67.6%) pts achieved MRD negativity at 10^-5. Among the 25 MRD negative pts, 11 (44%) were R-ISS stage 1, 13 (52%) stage 2 and one (4%) stage 3. Positron emission tomography-computed tomography (PET/CT) scans that were performed in 14 MRD (-) pts were negative for all pts except one. The markers of bone metabolism were measured in 22 pts. Only TRACP-5b levels showed a significant reduction (p=0.011) post KRd consolidation, which suggests a beneficial effect on bone resorption that must be further investigated. No new skeletal-related events (SREs) were reported. No patient has progressed whereas 37/39 (95%) are alive. One patient died due to staphylococcal pneumonia and another due to refractory thrombotic thrombocytopenic purpura complicated by brain hemorrhage and in-hospital infection during KRD. 7 (18%) pts experienced ≥grade 3 toxicities (mainly infections, TTP, fatigue, neutropenia, pneumonitis, hypocalcemia and increase of γGT and ALP). There were no new cases of peripheral neuropathy.

In conclusion, KRd consolidation with weekly carfilzomib, post ASCT, is highly effective and improves the quality of response by increasing MRD negativity rates. Although it is given for four cycles only, KRD consolidation reduces bone resorption and correlates with no SREs in the absence of bisphosphonates. Infections prophylaxis is strongly encouraged. This triplet combination should be further investigated as a potential consolidation regimen both for standard and high-risk pts.