Abstract: Patients with multiple myeloma (MM) carrying standard- or high-risk cytogenetic abnormalities (CAs) achieve similar complete response (CR) rates, but the later have inferior progression-free survival (PFS). This questions the legitimacy of CR as a treatment endpoint and represents a biological conundrum regarding the nature of tumor reservoirs that persist after therapy in high-risk MM. We used next-generation flow (NGF) cytometry to evaluate measurable residual disease (MRD) in MM patients with standard- vs high-risk CAs (n = 300 and 90, respectively) enrolled in the PETHEMA/GEM2012MENOS65 trial, and to identify mechanisms that determine MRD resistance in both patient subgroups (n = 40). The 36-month PFS rates were higher than 90% in patients with standard- or high-risk CAs achieving undetectable MRD. Persistent MRD resulted in a median PFS of ∼3 and 2 years in patients with standard- and high-risk CAs, respectively. Further use of NGF to isolate MRD, followed by whole-exome sequencing of paired diagnostic and MRD tumor cells, revealed greater clonal selection in patients with standard-risk CAs, higher genomic instability with acquisition of new mutations in high-risk MM, and no unifying genetic event driving MRD resistance. Conversely, RNA sequencing of diagnostic and MRD tumor cells uncovered the selection of MRD clones with singular transcriptional programs and reactive oxygen species–mediated MRD resistance in high-risk MM. Our study supports undetectable MRD as a treatment endpoint for patients with MM who have high-risk CAs and proposes characterizing MRD clones to understand and overcome MRD resistance. This trial is registered at www.clinicaltrials.gov as #NCT01916252.

Abstract: Assessing measurable residual disease (MRD) has become standard with many tumors, but the clinical meaning of MRD in multiple myeloma (MM) remains uncertain, particularly when assessed by next-generation flow (NGF) cytometry. Thus, we aimed to determine the applicability and sensitivity of the flow MRD-negative criterion defined by the International Myeloma Working Group (IMWG). PATIENTS AND METHODS In the PETHEMA/GEM2012MENOS65 trial, 458 patients with newly diagnosed MM had longitudinal assessment of MRD after six induction cycles with bortezomib, lenalidomide, and dexamethasone (VRD), autologous transplantation, and two consolidation courses with VRD. MRD was assessed in 1,100 bone marrow samples from 397 patients; the 61 patients without MRD data discontinued treatment during induction and were considered MRD positive for intent-to-treat analysis. The median limit of detection achieved by NGF was 2.9 × 10 −6 . Patients received maintenance (lenalidomide ± ixazomib) according to the companion PETHEMA/GEM2014MAIN trial. RESULTS Overall, 205 (45%) of 458 patients had undetectable MRD after consolidation, and only 14 of them (7%) have experienced progression thus far; seven of these 14 displayed extraosseous plasmacytomas at diagnosis and/or relapse. Using time-dependent analysis, patients with undetectable MRD had an 82% reduction in the risk of progression or death (hazard ratio, 0.18; 95% CI, 0.11 to 0.30; P 〈 .001) and an 88% reduction in the risk of death (hazard ratio, 0.12; 95% CI, 0.05 to 0.29; P 〈 .001). Timing of undetectable MRD (after induction v intensification) had no impact on patient survival. Attaining undetectable MRD overcame poor prognostic features at diagnosis, including high-risk cytogenetics. By contrast, patients with Revised International Staging System III status and positive MRD had dismal progression-free and overall survivals (median, 14 and 17 months, respectively). Maintenance increased the rate of undetectable MRD by 17%. CONCLUSION The IMWG flow MRD-negative response criterion is highly applicable and sensitive to evaluate treatment efficacy in MM.

Abstract: Patients with multiple myeloma (MM) may show patchy bone marrow (BM) infiltration and extramedullary disease. Notwithstanding, quantification of plasma cells (PCs) continues to be performed in BM since the clinical translation of circulating tumor cells (CTCs) remains undefined. PATIENTS AND METHODS CTCs were measured in peripheral blood (PB) of 374 patients with newly diagnosed MM enrolled in the GEM2012MENOS65 and GEM2014MAIN trials. Treatment included bortezomib, lenalidomide, and dexamethasone induction followed by autologous transplant, consolidation, and maintenance. Next-generation flow cytometry was used to evaluate CTCs in PB at diagnosis and measurable residual disease (MRD) in BM throughout treatment. RESULTS CTCs were detected in 92% (344 of 374) of patients with newly diagnosed MM. The correlation between the percentages of CTCs and BM PCs was modest. Increasing logarithmic percentages of CTCs were associated with inferior progression-free survival (PFS). A cutoff of 0.01% CTCs showed an independent prognostic value (hazard ratio: 2.02; 95% CI, 1.3 to 3.1; P = .001) in multivariable PFS analysis including the International Staging System, lactate dehydrogenase levels, and cytogenetics. The combination of the four prognostic factors significantly improved risk stratification. Outcomes according to the percentage of CTCs and depth of response to treatment showed that patients with undetectable CTCs had exceptional PFS regardless of complete remission and MRD status. In all other cases with detectable CTCs, only achieving MRD negativity (and not complete remission) demonstrated a statistically significant increase in PFS. CONCLUSION Evaluation of CTCs in PB outperformed quantification of BM PCs. The detection of ≥ 0.01% CTCs could be a new risk factor in novel staging systems for patients with transplant-eligible MM.

Abstract: In MM patients relapsing after MRD-negativity, the disease could reemerge from immature cells or from undetectable MRD. However, it remains unknown if immature cells have the same genetic background as MM plasma cells (PCs), as well as the amount of MRD that persists below the limit of detection (LOD) of next-generation techniques. To obtain further insight, we compared the biological landscape of MM PCs at diagnosis to that of CD34 progenitors, B cells and normal PCs isolated from patients with negative MRD by next-generation flow (NGF) after treatment. We performed whole-exome sequencing (WES, mean depth: 90x) with the 10XGenomics Exome Solution for low DNA-input as well as deep NGS of B-cell receptor immunoglobulin (BcR IG) gene rearrangements (mean, 69,975 sequences), in a total of 68 cell-samples isolated from the bone marrow (BM) of 7 MM patients with MRD-negativity by EuroFlow NGF after induction with VRD and auto-transplant (GEM2012MENOS65 trial). Patients with negative MRD were intentionally selected to avoid contamination with MM PCs during sorting of CD34 progenitors, B-cell precursors, mature B cells and normal PCs after induction and transplant. We investigated in these populations the presence of somatic mutations and clonotypic BcR Ig rearrangements detectable in MM PCs sorted at diagnosis, using peripheral blood T cells as germline control. We also performed WES in matched diagnostic MM PCs and MRD cells persisting after VRD induction in 14 cases as control. In another 6 patients with untreated MM, we performed single-cell RNA and BcR IG sequencing (scRNA/BcRIGseq) of total BM B cells and PCs (n=16,380) to investigate before treatment, if the clonotypic BcR IG sequence of MM PCs was detectable in other B cell stages defined by their molecular phenotype. We used multidimensional flow cytometry (MFC) to investigate the frequency of B cell clonality in BM samples from a larger series of 195 newly-diagnosed MM patients, prospectively enrolled in the GEM-CLARIDEX trial. Somatic mutations present in diagnostic MM PCs were detectable in the lymphopoiesis of 5/7 patients achieving MRD-negativity after treatment. In one case, out of 55 mutations present in diagnostic MM PCs, a single mutation in PCSK1N (VAF: 0.30) was detectable in normal PCs. In the other four patients, a total of 85 mutations were present in MM PCs and up to 10 (median VAF, 0.16) were found all the way from CD34 progenitors into B-cell precursors, mature B cells and normal PCs, but not in T cells. Of note, most mutations were reproducibly detected in each cell type after induction and after transplant. All somatic mutations shared by MM PCs and normal cells were non-recurrent, and genes recurrently mutated in MM (eg. ACTG1, ATM, DIS3, FAM46C, KRAS, LTB, MAX, TRAF3) were found in MM PCs but never in normal cells. Copy number alterations (CNA) were found only in MM PCs. By contrast, up to 513/827 (62%) mutations and 48/67 (72%) CNA were detectable in matched diagnostic MM PCs and persistent MRD cells, indicating that the few somatic variants present in normal cells were unlikely related to contaminating MRD below NGF's LOD. Accordingly, MM clonotypic BcR IG rearrangements were detectable in normal PCs (4/7patients) and in immature B cells (5/7 patients) but at much lower frequencies (mean of 0.02% in both). Of note, 9 additional clonotypes (mean 8.4%) were found in MM PCs of 5/7 patients (range, 1-3). scRNR/BcRIGseq unveiled that clonotypic cells were confined mostly but not entirely within PC clusters, and that in 1 patient another clonotype was detectable in mature B cells. Accordingly, using MFC we found in a larger series that 25/195 (13%) of newly-diagnosed MM patients display B-cell clonality (median of 0.7% BM clonal B cells, range 0.02%-6.3%). In conclusion, we show for the first time that MM patients bear somatic mutations in CD34 progenitors that specifically differentiate into the B cell lineage, likely before the disease onset. Because diagnostic, MRD (and relapse) MM PCs display great genetic similarity, these results suggest that undetectable MRD & lt;10-6 rather than normal cells with a few non-recurrent mutations are responsible for relapses after MRD-negativity. This study also challenges our understanding of myelomagenesis and clonal heterogeneity, and proposes that mutated lymphopoiesis may increase risk of developing B cell and PC oligoclonality, which precedes secondary driver mutations or CNA leading to the expansion of MM PCs. Disclosures Puig: Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Takeda, Amgen: Consultancy, Honoraria; The Binding Site: Honoraria; Janssen: Consultancy, Honoraria, Research Funding. Martinez-Lopez:BMS: Honoraria, Other: Advisory boards; Janssen: Honoraria, Other: Advisory boards and Non-Financial Support ; Amgen: Honoraria, Other: Non-Financial Support ; Celgene: Honoraria, Other: Advisory boards and Non-Financial Support ; Incyte: Honoraria, Other: Advisory boards; Novartis: Honoraria, Other: Advisory boards; VIVIA Biotech: Honoraria; F. Hoffmann-La Roche Ltd: Honoraria. Lahuerta:Takeda, Amgen, Celgene and Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Rosinol Dachs:Janssen, Celgene, Amgen and Takeda: Honoraria. Bladé:Jansen, Celgene, Takeda, Amgen and Oncopeptides: Honoraria. Mateos:EDO: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; GSK: Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive: Honoraria; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pharmamar: Membership on an entity's Board of Directors or advisory committees. San-Miguel:Amgen, Bristol-Myers Squibb, Celgene, Janssen, MSD, Novartis, Roche, Sanofi, and Takeda: Consultancy, Honoraria. Paiva:Amgen, Bristol-Myers Squibb, Celgene, Janssen, Merck, Novartis, Roche, and Sanofi; unrestricted grants from Celgene, EngMab, Sanofi, and Takeda; and consultancy for Celgene, Janssen, and Sanofi: Consultancy, Honoraria, Research Funding, Speakers Bureau.

Abstract: Background: Despite significant improvements in the treatment of MM, the outcome of patients with HR cytogenetics remains poor despite similar complete remission (CR) rates as compared to SR cases. Relapses among patients in CR are attributed to the persistence of MRD, but knowledge about the impact of MRD in patients with SR and HR cytogenetics, treated with modern therapies and monitored with next-generation techniques, is limited. Similarly, there is virtually no data about in vivo mechanisms of resistance in SR and HR MM; however, since MRD represents those very few cells that are resistant to treatment, it could be hypothesized that profiling MRD cells may shed light into the mechanisms of resistance in both SR and HR patients. Aim: To determine the clinical impact of MRD in MM patients with SR vs HR cytogenetics, and to identify transcriptional mechanisms determining MRD resistance by investigating the transcriptome of MRD cells in both patient subgroups. Methods: This study was conducted in a series of 390 patients enrolled in the PETHEMA/GEM2012 trial (6 induction cycles with VRD followed by ASCT and 2 courses of consolidation with VRD). FISH was analyzed on CD138 purified PCs at diagnosis. MRD was predefined to be prospectively assessed following induction, transplant and consolidation, using next-generation flow (NGF) according to EuroFlow. In 40 patients [28 with SR and 12 with HR cytogenetics: i.e., t(4;14), t(14;16) and/or del(17p)], diagnostic and MRD tumor cells persisting after VRD-induction were isolated by FACS according to patient-specific aberrant phenotypes. Due to the small number of sorted MRD cells (median of 25,600) we used a 3' end RNAseq method optimized for generating libraries from low-input starting material (MARSeq). Differential expression analyses were performed with DESeq2 R package. Results: At the latest time-point in which MRD was assessed, MRD-positive rates progressively increased (p =.006) from SR patients (148/300, 49%) to cases with t(4;14) (24/42, 57%) and del(17p) (29/38, 76%). Furthermore, MRD levels were significantly superior in patients with del(17p) compared to SR FISH (0.02% vs 0.006%, p =.009), while MRD levels in patients with t(4;14) (0.004%) were similar to those in SR MM. Only 10 patients had a t(14;16) and 4 were MRD-positive. Among patients achieving MRD-negativity ( 〈 2x10-6), 3-year progression-free survival (PFS) rates were similar for those with SR FISH, t(4;14) and del(17p) (90%, 100% and 89%; p 〉 .05). Conversely, 3-year PFS rates for MRD-positive patients decreased from those having SR FISH to those with t(4;14) and del(17p) (59%, 46% and 24%, respectively), with statistically significant differences between the first and the latest subgroups (p 〈 .001). Since clearance of MRD notably lowered the risk of relapse and persistence of MRD significantly shortened the PFS in each cytogenetic group (p ≤.001), we investigated the unique features of MRD cells persisting after VRD-induction by comparing their transcriptome to that of patient-matched tumor cells at diagnosis (n=40). Accordingly, MRD cells showed 763 genes significantly deregulated (Padj 〈 .05), including a cluster of proteasome subunits and proteasome related genes (i.e. PSMB5, PSMC3IP, BTRC, HUWE1, FBXL20 and TRIM69). Gene set enrichment analysis unveiled biologic determinants of MRD resistance such as the IL6-JAK-STAT signaling pathway in SR patients and the ROS pathway in HR patients (FDR 〈 0.1). Interestingly, the number of genes deregulated in MRD cells of SR patients was 9-fold higher than HR cases suggesting that, whereas in SR MM, a few tumor cells with specific gene regulatory networks may have higher probability to persist VRD induction, the presence of HR cytogenetic alterations is associated per se, with a transcriptional program that allows a few MRD cells to persist treatment. Conclusions: This is one of the largest studies integrating patients' cytogenetics and MRD status. Our results, based on intensive treatment and MRD monitoring using NGF, unveil that achieving MRD-negativity may overcome the poor prognosis of HR cytogenetics. By contrast, persistent MRD significantly reduces PFS rates, particularly in patients with del(17p). Interestingly, MRD cells from SR and HR patients may have different transcriptional mechanisms leading to VRD resistance, and further understanding of these could provide knowledge on how to eradicate MRD in both patient subgroups. Disclosures Puig: Takeda: Consultancy, Honoraria; Celgene: Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding. Garcia-Sanz:Affimed: Research Funding. Martinez-Lopez:BMS: Research Funding; Pfizer: Research Funding; Vivia: Honoraria; Celgene: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Novartis: Research Funding. Oriol:Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Rios:Amgen, Celgene, Janssen, and Takeda: Consultancy. De La Rubia:Ablynx: Consultancy, Other: Member of Advisory Board. Mateos:GSK: Consultancy, Membership on an entity's Board of Directors or advisory committees; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; GSK: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Lahuerta:Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees. Bladé:Janssen: Honoraria. San-Miguel:Amgen: Honoraria; BMS: Honoraria; Novartis: Honoraria; Sanofi: Honoraria; Celgene: Honoraria; Roche: Honoraria; Janssen: Honoraria.

Abstract: Background: Previous studies showed that MRD- pts after transplant may have detectable monoclonal protein through IFx, creating confusion regarding their prognostication. That said, MRD assessment in these pts was not performed with next generation techniques nor or in later time points. Additional discordances have been identified between multiparameter flow cytometry (MFC) and NGS, which were confirmed in recent analyses comparing NGF vs NGS. Aim: To characterize discordances between flow cytometry vs NGS and IFx through the investigation of immature B cells sharing the same B-cell receptor immunoglobulin (BcR IG) with MM cells. Methods: Progression-free survival (PFS) according to negative vs positive IFx was analyzed in 219 MRD- pts by MFC after transplant, enrolled in the GEM2000 and GEM2005MENOS65 trials. The same comparison was performed in 205 MRD- pts by NGF after consolidation in the GEM2012MENOS65 trial. MRD detection by NGS was compared to MFC or NGF in 140 and 104 cases, respectively. We performed NGS of BcR IG gene rearrangements (mean: 69,975 sequences) and WES (mean depth: 145x) in a total of 68 B cell samples isolated from the bone marrow (BM) of 7 MM MRD- pts by NGF after treatment (GEM2012MENOS65). These were intentionally selected to avoid contamination from MM plasma cells (PCs) during sorting of CD34 progenitors, B cell precursors, mature B cells and normal PCs. We investigated these populations for the presence of clonotypic BcR IG and somatic mutations detected in MM PCs sorted at diagnosis, using T cells as germline control. In another 10 untreated MM pts, we performed scRNA/BcRseq of total BM B cells and PCs (n=52,735), to investigate if the clonotypic BcR IG of MM PCs was detectable in other B cell stages defined by their molecular phenotype. Results: Among 219 MRD- pts by 4 color MFC after transplant, 76 (35%) showed positive IFx and identical PFS to those with negative IFx (medians of 63 vs 66 months, p=0.96). Similarly, 23/205 (11%) MRD- pts by NGF after consolidation showed positive IFx and identical PFS to those with negative IFx (4y rates of 87% vs 78.5%, p=0.35). Thus, albeit the higher sensitivity of NGF and the later time point (consolidation), approximately 1/10 MRD- pts by NGF continued showing positive IFx, and their outcome was as favorable as that of MRD- cases in CR. We then investigated discordances between flow cytometry and NGS. Among 35 MRD- pts by 4 color MFC, 21 (60%) were MRD+ by NGS, whereas 8/44 (18%) MRD- cases by NGF were MRD+ by NGS; only one of the latter 8 pts relapsed so far. Noteworthy, 9/29 MRD- pts by MFC or NGF showed MRD levels ≥10-4 by NGS, suggesting that other factors beyond sensitivity were accounting for the discordances between MRD assessed by MFC/NGF (in the PC compartment) vs NGS (in whole BM samples). NGS of BcR IG gene rearrangements in sorted BM cells from MRD- pts by NGF, uncovered the presence of MM clonotypes in normal PCs (4/7 pts) and in B cells (5/7 pts) at low frequencies (mean of 0.31% in both, range: 0.003% - 9.4%). These findings were confirmed by scRNA/BCRseq, which unveiled in 10/10 pts that clonotypic cells were confined mostly but not entirely within PC clusters. We next performed WES to investigate if genetic abnormalities present in MM PCs at diagnosis were detectable in the same BM cells sorted after treatment in MRD- pts. Surprisingly, 41/201 (20%) somatic mutations present in diagnostic MM PCs were detectable in CD34 progenitors (n=6/7), B-cell precursors (n=4/7), mature B cells (n=5/7) and phenotypically normal PCs (n=4/7). All somatic mutations shared by MM PCs and sorted BM normal cells were non-recurrent, and genes recurrently mutated in MM (ATM, DIS3, KRAS, LTB, MAX,) as well as copy number alterations (CNA) found in MM PCs, were undetectable in normal cells. Conclusions: Albeit more-sensitive NGF, 11% of MRD- pts continue showing positive IFx. This should not be regarded as a false-negative result, since these pts have similar outcome to those in CR and MRD-. Our findings also suggest that, at least in some pts, discordances between NGF and NGS could be attributed to immature clonotypic cells. However, these lack most somatic mutations and CNA found in MM PCs, and therefore cannot drive disease relapse. This would explain the favorable outcome of MRD- pts by NGF despite positive NGS. From a pathogenic standpoint, our study proposes that a mutated and clonally expanded lymphopoiesis precedes secondary driver mutations or CNA leading to the expansion of MM PCs. Disclosures García-Sanz: Janssen: Honoraria, Other: Travel/accommodations/expenses; Novartis: Consultancy; Amgen: Honoraria; Gilead: Other: Research grants, Research Funding; IVS (Biomed 2-Euroclonality): Patents & Royalties: and other intellectual property; Takeda: Consultancy, Honoraria, Other: Travel/accommodations/expenses. Mateos:Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Regeneron: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive: Honoraria, Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Honoraria. Chatzidimitriou:Janssen: Research Funding. San-Miguel:Bristol-Myers Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Karyopharm: Consultancy, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Consultancy, Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Roche: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; MSD: Consultancy, Membership on an entity's Board of Directors or advisory committees. Paiva:Amgen: Honoraria; Janssen: Consultancy, Honoraria; Karyopharm: Consultancy, Honoraria; Kite: Consultancy; SkylineDx: Consultancy; Takeda: Consultancy, Honoraria, Research Funding; Roche: Research Funding; Adaptive: Honoraria; Sanofi: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding, Speakers Bureau.

Abstract: Background: MRD is an established biomarker to evaluate treatment efficacy, define patients at risk based on persistent MRD, and eventually, act as surrogate for prolonged survival based on sensitive MRD-negative definitions. Accordingly, the IMWG has developed criteria for MRD-negativity defined by next-generation sequencing, NGF or PET/CT, and has recommended their inclusion in clinical trials. Notwithstanding, most flow cytometry results have been obtained using less sensitive methods and in fact, there is no data about the impact of NGF-based MRD assessment in clinical trials. Aim: To define the feasibility, sensitivity and clinical impact of NGF-based MRD assessment in the phase III PETHEMA/GEM2012 trial. Methods: A total of 458 patients were enrolled into the PETHEMA/GEM2012 trial. MRD was predefined to be prospectively assessed at three time-points: after six induction cycles with bortezomib, lenalidomide, and dexamethasone (VRD), after HDT/ASCT, and after two courses of consolidation with VRD. MRD monitoring was performed blinded for clinical outcomes in four PETHEMA/GEM laboratory cores, and data was centralized for MRD analyses. MRD assessment was performed following EuroFlow SOPs in a total of 1,134 bone marrow (BM) samples from 419 patients. The 39 cases without MRD assessment had suboptimal response to induction and were thus considered as MRD+ for intention-to-treat analyses. Noteworthy, in 14 BM samples with undetectable MRD, B-cell precursors, erythroblasts and mast cells represented & lt;0.01% of BM cells, and these samples were thus considered as hemodiluted and inadequate for MRD assessment. The limit of detection (LOD) was determined for each of the 1,117 BM samples representative for MRD assessment, according to the formula: (20/nucleated viable cells) x 100; the median LOD achieved by NGF in the PETHEMA/GEM2012 trial was of 3x10-6. Results: Overall, 225/458 (49%) patients had undetectable MRD at the latest time-point in which MRD was assessed and were thus classified as MRD-. Conversely, 233/458 (51%) cases remained MRD+: 28% with ≥10-4 MRD, 12% with 10-5 MRD, and 11% with 10-6 MRD. Detailed analyses of MRD kinetics in 320 patients with available MRD results at all three time-points, showed that the percentage of MRD- patients increased from 35% into 54% and 58% after induction, HDT/ASCT and consolidation, respectively. Furthermore, a restricted analysis among MRD+ patients showed that whereas after induction only 8% of them had MRD levels as low as 10-6, subsequent intensification with HDT/ASCT and consolidation could reduce MRD levels down to 10-6 in 32% of MRD+ cases. Progression-free survival (PFS) rates at 3-years were of 92%, 70%, 54% and 44% for patients being MRD-negative, MRD+ 10-6, 10-5 and ≥10-4, respectively (P & lt;.001; Figure). Thus far, only 6/225 (3%) MRD- patients have relapsed; strikingly, all 6 cases had extramedullary plasmacytomas at diagnosis, all relapsed with extramedullary plasmacytomas, and only 2 had concomitant serological relapse. The favorable outcome of MRD- patients encouraged us to investigate the impact of MRD negativity in both standard- and high-risk patients defined by FISH [i.e.: t(4;14), t(14;16), and/or del(17p)]. Even though MRD- rates were significantly inferior in patients with high- vs standard-risk FISH (37% vs 50%, respectively; P=.03), 3-year PFS rates were similar between patients with high- and standard-risk FISH reaching MRD-negativity (94% and 91%, respectively; P=.56); by contrast, MRD+ cases with high- and standard- risk FISH had median PFS of 27 and 35 months, respectively (P=.025). Conclusions: This is the largest study of MRD monitoring in MM based on the total number of samples analyzed (n=1,134). Our results show that NGF-based MRD assessment is feasible in large multicenter clinical trials, is highly-sensitive, and allows the identification of hemodiluted BM samples inadequate for MRD assessment. Risk of relapse among MRD-negative patients was remarkably reduced (3%), and was particularly related to the reappearance of extramedullary plasmacytomas, which urges the need for combined cellular and imaging MRD monitoring in these patients; by contrast, even MRD levels as low as 10-5 and 10-6 conferred significantly inferior PFS. Overall, this study defines MRD-negativity as the most relevant clinical endpoint for both standard- and high-risk transplant-eligible MM patients. Figure Figure. Disclosures Paiva: Sanofi: Consultancy, Honoraria, Research Funding; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Honoraria; Merck: Honoraria; Novartis: Honoraria; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; EngMab: Research Funding. Oriol: Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: sponsored symposia, Speakers Bureau; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: sponsored symposia, Speakers Bureau; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: sponsored symposia; Celgene: Speakers Bureau. de la Rubia: Janssen: Other: Honoraria; Amgen: Other: Honoraria; Celgene: Other: Honoraria. Rosinol: Celgene: Honoraria; Janssen: Honoraria. Mateos: Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Lahuerta: Amgen: Honoraria; Celgene: Honoraria; Janssen: Honoraria. San Miguel: Roche: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Consultancy, Membership on an entity's Board of Directors or advisory committees; MSD: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees.

Abstract: Risk of developing myelodysplastic syndrome (MDS) is significantly increased in both multiple myeloma (MM) and monoclonal gammopathy of undetermined significance, suggesting that it is therapy independent. However, the incidence and sequelae of dysplastic hematopoiesis at diagnosis are unknown. Here, we used multidimensional flow cytometry (MFC) to prospectively screen for the presence of MDS-associated phenotypic alterations (MDS-PA) in the bone marrow of 285 patients with MM enrolled in the PETHEMA/GEM2012MENOS65 trial (#NCT01916252). We investigated the clinical significance of monocytic MDS-PA in a larger series of 1252 patients enrolled in 4 PETHEMA/GEM protocols. At diagnosis, 33 (11.6%) of 285 cases displayed MDS-PA. Bulk and single-cell–targeted sequencing of MDS recurrently mutated genes in CD34+ progenitors (and dysplastic lineages) from 67 patients revealed clonal hematopoiesis in 13 (50%) of 26 cases with MDS-PA vs 9 (22%) of 41 without MDS-PA; TET2 and NRAS were the most frequently mutated genes. Dynamics of MDS-PA at diagnosis and after autologous transplant were evaluated in 86 of 285 patients and showed that in most cases (69 of 86 [80%]), MDS-PA either persisted or remained absent in patients with or without MDS-PA at diagnosis, respectively. Noteworthy, MDS-associated mutations infrequently emerged after high-dose therapy. Based on MFC profiling, patients with MDS-PA have altered hematopoiesis and T regulatory cell distribution in the tumor microenvironment. Importantly, the presence of monocytic MDS-PA at diagnosis anticipated greater risk of hematologic toxicity and was independently associated with inferior progression-free survival (hazard ratio, 1.5; P = .02) and overall survival (hazard ratio, 1.7; P = .01). This study reveals the biological and clinical significance of dysplastic hematopoiesis in newly diagnosed MM, which can be screened with moderate sensitivity using cost-effective MFC.