Analysis of treatment efficacy in the GEM-CESAR trial for high-risk smoldering multiple myeloma patients: Comparison between the standard and IMWG MRD criteria and QIP-MS including FLC (QIP-FLC-MS).

Abstract

8512 Background: The GEM-CESAR trial is a potentially curative strategy for high-risk smoldering multiple myeloma (HRsMM) patients (pts) in which the primary endpoint is the achievement of sustained minimal residual disease (MRD) negativity in the bone marrow (BM) by next generation flow (NGF). The value of BM MRD assessment in MM is proven, but alternative, non-invasive methods, accurately reflecting disease burden are needed. Methods: Pts received six 4-week cycles of KRd as induction (K:36mg/m2 twice weekly, R: lenalidomide 25mg po od days 1-21 and d:dexamethasone 40mg po weekly) followed by melphalan 200mg/m2, two further cycles of KRd as consolidation and up to 2 years of Rd (R:10mg/d, d:20mg/week). Efficacy was analyzed in parallel in BM samples by NGF and in serum by SPEP/IFE and QIP-MS/QIP-FLC-MS in 52 out of the 90 pts enrolled in the trial. Standard and MRD responses were carried out as per the IMWG guidelines. For QIP-MS serum immunoglobulins were purified using polyclonal antibodies (anti-IgG, -IgA, -IgM, -total κ and -total λ light chain, -free κ and -free λ light chain). Mass spectra were generated on a MALDI-TOF-MS system. Results: Overall response rate (ORR) was 98% post-induction, 98% post-ASCT, and 100% post-consolidation; 38.4%, 61.5% and 68.6% of pts reached ≥ complete response at each time-point and, among them, 23%, 44% and 55% achieved flow MRD-negativity. Using the combination of QIP-MS/QIP-FLC-MS, the percentage of pts without detectable disease at each timepoint lowered to 12%, 27% and 38% reflecting the higher sensitivity of the method. Against NGF, QIP-MS/QIP-FLC-MS provided negative predictive values of 67%, 92% and 89% (p = 0,0206; p < 0,001; p = 0,003) and identified disease in 95%, 97% and 92% of pts that were positive by NGF-MRD at each respective timepoint. Three pts from this cohort have progressed so far: two were NGF+/MS+ at the three timepoints whilst 1 remained NGF- but QIP-MS/FLC-MS+ throughout. Conclusions: The GEM-CESAR treatment strategy induces a high ORR in HRsMM pts, and the % of cases achieving flow-MRD negativity post-ASCT meets the primary endpoint of the trial. The combined use of QIP-MS and FLC-MS offers higher sensitivity relative to standard methods and may provide relevant information about the right timing for performing a BM aspirate/biopsy. Clinical trial information: NCT02415413 .