Curativestategy (GEM-CESAR) for High-Risk Smoldering Myeloma (SMM): Carfilzomib, Lenalidomide and Dexamethasone (KRd) As Induction Followed By HDT-ASCT, Consolidation with Krd and Maintenance with Rd

Introduction:SMM is an asymptomatic and heterogeneous plasma cell disorder. The Spanish Myeloma Group demonstrated that patients at high risk of progression benefit from early treatment with Rd. In addition, our preliminary results of the curative approach (GEM-CESAR) showed encouraging results (Mateos ASH 2017).

Aim: The primary end-point was to evaluate the Minimal Residual Disease negative (MRD-ve) rate by next generation flow (NGF) after induction and ASCT and the sustained MRD-ve rate at 3 and 5 yrs after ASCT as secondary end-points. Our aim was to increase the MRD -ve rate from 34% (reported in NDMM patients after VTD and ASCT) to 50%. As all patients have completed induction and ASCT, we report the results of the primary end point, efficacy and safety after induction and ASCT.

Methods: In this phase II single arm trial, 90 SMM patients at high-risk of progression (>50% at 2 yrs), younger than 70 yrs and transplant candidates were included. The high risk was defined by the presence of both ≥PC 10% and MC ≥3g/dL (Mayo criteria) or ifonly one criterion was present, patients must have a proportionof aberrant PCs within the total PCsBM compartment by immunophenotypingof 95% plus immunoparesis (Spanish criteria). Asymptomatic MM patients with any of the three biomarkers recently included into the definition of active MM were allowed to be included. Induction therapy consisted on six 4-weeks cycles of KRd in which K was given at dose of 36 mg/m²twice per week plus R at dose of 25 mg on days 1-21 and dexamethasone at dose of 40 mg weekly. Melphalan at dose of 200 mg/m²followed by ASCT was given as intensification therapy and three months later, patients received two KRd consolidation cycles followed by maintenance with R at dose of 10 mg on days 1-21 plus dex at dose of 20 mg weekly for up to 2 yrs

Results: Between June 2015 and June 2017, the 90 SMM patients at high risk of progression were recruited. Twenty-eight pts (32%) shared at least one of the new biomarkers predicting imminent risk of progression to MM.

The primary end point of the trial was met, since 55% of the patients who completed induction and ASCT achieved MRD -ve by NGF (sensitivity 3 x 10^-6). Upon analyzing the results after induction, 88 patients completed the 6 induction cycles and were evaluable for response (two patients early discontinued): the ORR was 98% including 41% of ≥CR (32% sCR and 9% CR) and 41% of VGPR rate. Two patients were mobilization failures and one patient rejected ASCT. Two additional patients experienced biological progression before ASCT and went off the study. Eighty-three patients, therefore, proceeded to HDT-ASCT and were evaluable at day +100: the ORR was 100% including ≥CR in 63% of the patients (51% sCR and 12% CR) and VGPR rate in 23%. The MRD-ve rate increased from 31% after induction to 55% with the ASCT. No differences in outcome have been observed according neither to the definition of high risk (Mayo or Spanish model) nor ultra high risk SMM.

Concerning toxicity, during induction, G3-4 neutropenia and thrombocytopenia were reported in 5 (6%) and 10 pts (11%), respectively. G3-4 infections were the most frequent non-hematological AE observed in 16 pts (18%), followed by skin rash in 8 pts (9%). One patient reported G1 atrial fibrillation and another cardiac failure secondary to respiratory infection. Three patients reported hypertension (G2 in two and G3 in one). Thirteen patients required lenalidomide dose reduction whilst carfilzomib was not reduced in any patient. In four patients, dexamethasone was reduced. In all but two of the pts, PBSC collection was successful with a median of 4.10 x 10⁶/Kg CD34 cells collected. All patients engrafted. Consolidation and maintenance phases are ongoing.

After a median follow-up of 17 months (5-36), 94% of patients remain alive and free of progression and 97% of them alive. Three patients experienced biological progression and discontinued the study: one of them was refractory to the rescue therapies and died and the other two are receiving rescue therapies. One additional patient died early during induction due to a massive ischemic stroke unrelated to the treatment.

Conclusions: Although longer follow-up is required, this "curative strategy for high risk SMM" continues being encouraging with an acceptable toxicity profile. The study has met its primary endpoint. The depth of response improved over the treatment: 63% of patients who completed induction and ASCT achieved ≥CR with a MRD-ve rate of 55%.