Abstract: Background: Since survival in AL mainly depends on the extent of organ involvement of patients at presentation, early diagnosis and risk stratification are key to improve patients' outcome. Therefore, together with surrogates of organ involvement, biomarkers identifying patients with MGUS or MM at greater risk of developing AL would be highly valuable to prevent organ damage, to maximize therapeutic efficacy and to improve outcomes in AL. Aim: To investigate the value of multidimensional flow cytometry (MFC) for simultaneous fast diagnostic screening of plasma cell (PC) clonality and risk stratification, as well as to identify immunophenotypic markers useful for the selection of patients with monoclonal gammopathies candidates for monitoring of pre-symptomatic organ damage related to AL. Methods: We used MFC to characterize a large series of patients with newly-diagnosed (ND) AL (N=94) vs MGUS (N=20) and NDMM (N=52), as well as age-matched healthy adults (HA, N=30). For each patient with AL, automated risk stratification was performed using principal component analysis (PCA) based on the relative frequency of bone marrow (BM) PCs, plus the percentage of clonal and normal PCs within the whole BM PC compartment, vs a database containing information on the same three parameters from a total of 1,774 patients, including 497 MGUS and 1,227 NDMM. In parallel, immunophenotypic protein expression profiles (iPEP) of AL patients were clustered using t-SNE, and the comparison between the iPEP of clonal PCs from patients with AL vs MGUS and MM cases was performed using canonical-correlation analysis (CCA). To identify additional immunophenotypic hallmarks of AL, the BM cellular composition in HA, MGUS, AL and MM patients was compared using 2-dimensional minimum spanning tree (MST) force-directed classification to determine the distance among individual cases. Results: PC clonality was detected by MFC in 93/94 (99%) AL patients, whereas an M-component was detectable in 96% of cases by electrophoresis, immunofixation and sFLC. PCA as defined above, identified AL patients displaying an MM-like (n=6) and an MGUS-like (n=38) signature, as well as 49 cases with an intermediate signature between the MGUS and MM reference datasets. Multivariate analysis of baseline prognostic factors for survival, including patients' age, number of organs involved, Mayo staging, the percentage of BM PCs based on cytomorphology and eligibility for ASCT, showed that having an intermediate- or an MM-like profile had an independent adverse effect on patients' progression-free (PFS) and overall survival (OS) (HR:3.4; P≤.02). t-SNE based on the iPEP of clonal PCs revealed two major clusters of AL patients with significantly different PFS, defined by opposite patterns of expression for CD45, CD56 and CD138 (P≤.02). CCA of tumor iPEP showed partial overlap between AL vs MGUS and MM, with progressively higher percentages of cases with a CD38lo, CD45-ve, CD81-ve and CD138lo iPEP being observed from MGUS to AL and MM. In contrast, AL patients displayed significantly lower reactivity for CD56 (P≤ .03). Further characterization of the BM cellular composition allowed the systematic assessment of 16 cell populations and 18 phenotypic parameters that, by MST, mapped AL in between MGUS and MM. Of note, while AL patients displayed a predominantly-clonal PC compartment in the absence of an MM-like tumor PC expansion, the percentage of B-cell precursors was consistently lower in AL patients than in HA, MGUS and MM (P=.004). Thus, using optimal cut-off values to discriminate between AL vs MGUS and MM, we built a scoring model based on the presence of 〈 100% CD56+ve clonal PCs, 〈 0.1% B-cell precursors, 〉 80% clonal PCs within total BM PCs and 〈 2% BM PCs. Overall, a significant (P 〈 .001) association was found between a progressively higher score and the diagnosis of AL, with a 74% accurate classification based on ROC analysis (AUC of 0.74; 95% CI = 0.66 - 0.82; P 〈 .001) of the performance of the scoring model. Conclusions: We demonstrate the value of MFC for fast diagnostic screening of PC clonality in AL and simultaneous automated patient risk-stratification, based on the BM tumor burden and PC phenotype. In addition, our results also provide new immunophenotypic markers for the identification of patients with monoclonal gammopathies that are candidates for monitoring of pre-symptomatic organ damage related to AL. Disclosures Puig: Janssen: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria; Celgene: Honoraria, Research Funding. Ocio:Array Pharmaceuticals: Research Funding; Sanofi: Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Pharmamar: Consultancy; BMS: Consultancy; AbbVie: Consultancy; Janssen: Consultancy, Honoraria; Seattle Genetics: Consultancy; Mundipharma: Research Funding; Takeda: Consultancy, Honoraria; Novartis: Consultancy, Honoraria. Oriol:Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; 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; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. De La Rubia:Ablynx: Consultancy, Other: Member of Advisory Board. Martinez Lopez:Janssen: Research Funding, Speakers Bureau; Celgene: Research Funding, Speakers Bureau; Novartis: Research Funding, Speakers Bureau; Bristol Myers Squibb: Research Funding, Speakers Bureau. Mateos:Amgen: 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; 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; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; GSK: Consultancy, 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; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Lahuerta:Janssen: Honoraria; Celgene: Honoraria; Amgen: Honoraria.

Abstract: Abstract 614 Smoldering MM (sMM) is a plasma cell (PC) disorder defined by the presence of ≥10% of PC and/or a serum M-component (MC) ≥3g/dl without end-organ damage. Recent studies have identified a subgroup of sMM at high risk of progression to active MM ( 〉 50% at 2 y): patients with both PC ≥10% & MC ≥3g/dl (Kyle R. NEJM 2007) or ≥95% aberrant PC (aPC) by immunophenotyping (Pérez E. Blood 2007) or abnormal FLCs (Dispenzieri A. Blood 2008). Standard of care for sMM is monitoring without treatment until disease progression. Several small studies have explored the value of early treatment with either conventional agents (melphalan/prednisone) or novel drugs (thalidomide, interleukin-1b), with no clear benefit. It should be noted that these trials didn't focus on high-risk sMM. In this phase III trial we investigated whether early treatment prolongs the time to progression (TTP) in sMM patients at high risk of progression to active MM. Patients were randomized to receive Len-dex versus no treatment. The high risk population was defined by the presence of both PC ≥10% and MC ≥3g/dl or if only one criterion was present, patients must have a proportion of aPC within the total PCBM compartment by immunophenotyping of ≥95% plus immunoparesis. 120 patients are planned to be recruited. The 60 patients randomized to the Len-dex arm receive nine four-weeks cycles of lenalidomide at dose of 25 mg daily on days 1-21 plus dexamethasone at dose of 20 mg daily on days 1-4 and 12-15 (total dose: 160mg) (induction phase); subsequently maintenance with Lenalidomide at dose of 10 mg on days 1-21 every two months administered until disease progression. Between October 2006 and June 2008, 80 patients were randomized. In this interim analysis, we present the first 40 patients recruited. According to baseline characteristics, both groups were well balanced. In an ITT analysis (n=40), based on IMWG criteria, the overall response rate was 90%, including 53% PR, 21% VGPR, 11% CR and 5% sCR. If we select the group of 16 patients who completed the nine cycles, the ORR was 100%, including 27% VGPR, 13% CR and 7% sCR. After a median follow-up of 16 months (range:12-20), no disease progression was observed in the Len-dex arm, while 8 patients progressed to active MM in the therapeutic abstention arm with a median TTP from inclusion in the trial of 17.5 months (p 〈 0.002). It should be noted that 6 of these 8 patients developed bone lesions as a symptom of active MM. As far as toxicity is concerned, no G4 adverse events (AEs) were reported with Len-dex; 1 pt developed G3 anemia, 2 patients G3 asthenia, 1 pt G3 diarrhea and 3 patients G3 DVT. Serious AEs occurred in 5 patients, 3 of these were dexamethasone-related (GI bleeding, delirium and glaucoma) and 2 were lenalidomide-related (two infections). Two SAEs lead to early discontinuation of the treatment (infection and delirium), and another 2 additional patients discontinued at pt's request. Four patients needed to reduce lenalidomide from 25 to 15 mg due to non-hematological AEs (asthenia (2), diarrhea (1) and GI bleeding (1). In conclusion, these preliminary results show that in sMM patients at high-risk for progression to active MM, delayed treatment is associated with early progression (median time 17.5 months) with bone disease, while so far Len-dex has been able not only to prolong the TTP (without any progression so far) but also to induce CRs with a manageable and acceptable toxicity profile. Disclosures: Mateos: Celgene: Honoraria. Off Label Use: Lenalidomide is not approved for the treatment of smoldering multiple myeloma patients. de la Rubia:Janssen-Cilag: Honoraria; Celgene: Honoraria. Rosiñol:Janssen-Cilag: Honoraria; Celgene: Honoraria. García-Laraña:Janssen-Cilag: Honoraria; Celgene: Honoraria. Palomera:Janssen-Cilag: Honoraria; Celgene: Honoraria. de Arriba:Janssen-Cilag: Honoraria; Celgene: Honoraria. Quintana:Celgene Corporation: Employment. Garcia:Celgene Corporation: Employment. San-Miguel:Celgene Corporation: Honoraria, Speakers Bureau.

Abstract: Abstract 1935 Smoldering Multiple Myeloma (SMM) is an asymptomatic proliferative disorder of plasma cells (PCs) defined by a serum monoclonal component (MC) of 30 g/L or higher and/or 10% or more plasma cells in the bone marrow (BM), but no evidence of end-organ damage. There are several risk factors predicting high-risk of progression to symptomatic disease ( 〉 50% at 2 years): 〉 10% of PCs in BM, serum MC 〉 30g/L, 〉 95% aberrant PCs by immunophenotyping, or abnormal free-light chains. Standard of care of SMM is close follow-up without treatment until progression disease. Several trials have evaluated the role of early treatment with convencional agents (melphalan), bisphosphonates and novel agents (thalidomide, anti-IL1a), with no clear benefit, but they didn't focus on high-risk patients. In this phase III trial, SMM patients at high-risk of progression were randomized to receive Len-dex as induction followed by Len alone as maintenance vs no treatment in order to evaluate whether the early treatment prolongs the time to progresión (TTP) to symptomatic disease. The high risk population was defined by the presence of both 〉 PC 10% and MC 〉 30g/L or if only one criterion was present, patients must have a proportion of aberrants PCs within the total PCsBM compartment by immunophenotyping of 95% plus immunoparesis. Len-dex arm received an induction treatment consisting on nine four-weeks cycles of lenalidomide at dose of 25 mg daily on days 1–21 plus dexamethasone at dose of 20 mg daily on days 1–4 and 12–15 (total dose: 160mg), followed by maintenance until progression disease with Lenalidomide at dose of 10 mg on days 1–21 every two months (ammended in May 2010 into monthly). The 124 planned patients were recruited between October 2006 and June 2010, and 118 were evaluables (three in Len-dex and three in therapeutic abstention arm didn't meet inclusion criteria). This second interim analysis was planned when all patients were recruited. According to baseline characteristics, both groups were well balanced. On an ITT analysis (n=57), based on IMWG criteria, the overall response rate during induction therapy was 75%, including 51% PR, 12% VGPR, 5% CR and 7% sCR. If we select the group of 33 patients who completed the nine induction cycles, the ORR was 91%, including 15% VGPR, 9% CR and 9% sCR. After a median of 8 cycles of maintenance therapy (1-15), the sCR increased to 16%. After a median follow-up of 16 months (range:1-33), four patients progressed to symptomatic disease in the Len-dex arm: two of them during maintenance therapy after 24 and 28 months from inclusion and the other two progressed 3 and 8 months after early discontinuation of the trial due to personal reasons. In addition, nine patients have developed biological progression during maintenance, but in all but one of these, Len has been able to control the disease without CRAB symptoms (median of 9·5 months (1-18)). In the therapeutic abstention arm, 21 out of 61 patients progressed to active MM. The estimated hazard ratio was 6·7 (95%CI= 2·3-19·9), corresponding to a median TTP from inclusion of 25 months for the not treatment arm vs median not reached in the treatment arm (p 〈 0.0001). It should be noted that 10 out of these 21 patients developed bone lesions as a symptom of active MM. Deaths in the Len-dex and no treatment arms were 1 and 2, respectively (p=0·6). As far as toxicity is concerned, during induction therapy, no G4 adverse events (AEs) were reported with Len-dex; 1 pt developed G3 anemia, 4 patients G3 asthenia 2 patients G3 diarrhea and 1 patient G3 skin rash; 3 patients developped G2 DVT. During maintenance, no G4 AEs were reported and only 1 patient developed G3 infection. In conclusion, this second interim analysis shows that in high-risk SMM patients, delayed treatment resulted in early progression to symptomatic disease (median 25 months), while Len-dex as induction followed by Len as maintenance significantly prolonged the TTP (HR: 6·7), with excelent tolerability; moreover, biological progressions occurring under maintenance have remained controlled over a prolonged period of time. Disclosures: Mateos: Celgene: Honoraria. Off Label Use: Lenalidomide is not approved for the treatment of smoldering multiple myeloma. De La Rubia:Celgene: Honoraria. Rosiñol:Celgene: Honoraria. Lahuerta:Celgene: Honoraria. Palomera:Celgene: Honoraria. Oriol:Celgene: Honoraria. Garcia-Laraña:Celgene: Honoraria. Hernández:Celgene: Honoraria. Leal-da-Costa:Celgene: Honoraria. Alegre:Celgene: Honoraria. Quintana:Celgene: Employment. Baquero:Celgene: Employment. García:Celgene: Honoraria. San Miguel:Celgene: Honoraria.

Abstract: Background: SMM is a plasma cell (PC) disorder defined by the presence of at least 10% of PC and/or a serum M-component (MC) at least 3g/dl without end-organ damage. Due to the nature of the disease, SMM pts at high risk of progression to active MM ( 〉 50% at 2 yrs) have been identified using different criteria: bone marrow infiltration by 〉 10% of PCs & MC 〉 3g/dl (Kyle,NEJM 2007), or 〉 95% aberrant PC (aPC) by immunophenotyping plus immunoparesis (Pérez, Blood 2007), or abnormal FLCs (Dispenzieri,Blood 2008). The current standard of care for SMM is watchful waiting until disease progression. Although several small randomized studies have explored the value of early treatment with either conventional agents (melphalan/prednisone) or thalidomide, bisphosphonates, they showed no significant benefit. It should be noted that these trials did not focus on high-risk SMM. In 2007, the Spanish Myeloma Group initiated a randomized, phase III trial comparing lenalidomide (R) + low-dose dexamethasone (Rd) vs observation in high-risk SMM pts. After a median follow-up of 40 months, early treatment with Rd showed to be superior in terms of time to progression to active disease and overall survival (OS) (Mateos, NEJM 2014). Here we present an update after long-term median follow-up of 5 years. Pts and Methods: 119 pts with high-risk SMM were enrolled and randomized to Rd vs. observation. Pts in the treatment group received an induction regimen (lenalidomide 25 mg/day on days 1 to 21 plus dexamethasone 20 mg/day on days 1 to 4 and 12 to 15, at 4-week intervals for nine cycles) followed by a maintenance regimen (lenalidomide 10 mg/day on days 1 to 21 of each 28-day cycle). Maintenance therapy was initially given until disease progression, but an amendment limited the total treatment duration (induction plus maintenance) to 2 years, and the addition of dexamethasone (20 mg on days 1 to 4 of each cycle) for pts who developed asymptomatic biological progression during maintenance ( 〉 25% of increase in monoclonal component with no symptoms). The primary endpoint was time to progression to symptomatic disease (TTP), secondary endpoints included OS, response, and safety. Results: After a median follow-up of 64 months (range: 49-81), progression to symptomatic disease occurred in 23% of pts with Rd vs. 85% for the pts in the observation arm. Long term follow-up with early Rd treatment continues to show a significant benefit in TTP to active disease vs. watchful waiting (median TTP not reached vs. 21 months, HR= 6.21; 95% CI: 3.1-12.7, p 〈 0.0001). During maintenance therapy, 24 pts in the Rd arm experienced asymptomatic biological progression and low-dose dexamethasone was added in 18 pts. With a median follow-up of 50 months from biological progression, disease remains under control in 10 out of these 18 pts and they continue on therapy with lenalidomide plus dexamethasone at low doses. Pts who progressed to symptomatic disease and required to start systemic therapy were also followed for survival, and the percentage of pts who remain alive at 5 years after progression to active disease is 83% in the Rd vs. 58% in the observation arm. OS continues to be significantly longer with Rd vs. with the observation arm: 93% of the pts who received early treatment with Rd remain alive vs. 67% in the watchful waiting arm, (HR= 4.35, 95% CI 1.5-13.0, p=0.008). Only four pts died in the Rd arm, whilst 17 deaths occurred in the observation arm. In the Rd arm, only one patient’s death was considered treatment-related (pneumonia); disease progression was the cause of death in two pts and bronchoaspiration as consequence of surgery-related complication in the fourth pt. In the observation arm, disease progression was the most frequent cause of death, in 76% of the pts. As far as toxicity is concerned, no new second primary malignancy (SPM) occurred: four SPM were reported in 4 of the 62 pts with Rd (6%) and in 1 of the 63 pts in the observation group (2%). Conclusions: After long-term follow-up, Rd in high risk SMM pts as early treatment with Rd continued to show a significant reduction of not only in the risk of progression to active disease but also the risk of death. In addition, the long post relapse survival observed among pts who received early treatment with Rd and subsequently progressed to symptomatic disease indicate that this strategy does not induce more resistant clones. Disclosures Mateos: Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees. Off Label Use: Lenalidomide as first-line combination therapy for AL amyloidosis.. De La Rubia:Janssen: Honoraria; Celgene: Honoraria. Rosiñol:Janssen: Honoraria; Celgene: Honoraria. Oriol:Celgene Corporation: Consultancy. Blade:Janssen: Honoraria; Celgene: Honoraria. Lahuerta:Janssen: Honoraria; Celgene: Honoraria.

Abstract: Although light-chain amyloidosis (AL) and multiple myeloma (MM) are characterized by tumor plasma cell (PC) expansion in bone marrow (BM), their clinical presentation differs. Previous attempts to identify unique pathogenic mechanisms behind such differences were unsuccessful, and no studies have investigated the differentiation stage of tumor PCs in patients with AL and MM. We sought to define a transcriptional atlas of normal PC development in secondary lymphoid organs (SLOs), peripheral blood (PB), and BM for comparison with the transcriptional programs (TPs) of tumor PCs in AL, MM, and monoclonal gammopathy of undetermined significance (MGUS). Based on bulk and single-cell RNA sequencing, we observed 13 TPs during transition of normal PCs throughout SLOs, PB, and BM. We further noted the following: CD39 outperforms CD19 to discriminate newborn from long-lived BM-PCs; tumor PCs expressed the most advantageous TPs of normal PC differentiation; AL shares greater similarity to SLO-PCs whereas MM is transcriptionally closer to PB-PCs and newborn BM-PCs; patients with AL and MM enriched in immature TPs had inferior survival; and protein N-linked glycosylation–related TPs are upregulated in AL. Collectively, we provide a novel resource to understand normal PC development and the transcriptional reorganization of AL and other monoclonal gammopathies.

Abstract: MM patients are living longer with increasingly effective therapies, but long-term complications including second primary malignancies (SPMs) are becoming new challenges in designing optimal patient care. It has been demonstrated in large studies that amongst others, risk is particularly high for SPMs such as myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). Importantly, such increased risk of MDS/AML has also been observed in MGUS patients, suggesting that increased risk for MDS/AML may not only be treatment related but inheritably high in MGUS/MM. Thus, there is need to investigate for biomarkers that uncover cellular alterations predisposing for higher risk of MDS/AML in MM. Here, we started by investigating in 312 newly diagnosed MM patients the presence of MDS-like phenotypic abnormalities (MDS-PA) in bone marrow (BM) neutrophil, monocytic, and erythroid lineages, using multidimensional flow cytometry 8 color combinations (CD138, CD27, CD38, CD56, CD45, CD19, CD117, CD81; and HLADR, CD45, CD36, CD13, CD34, CD117, CD11b, CD71). Up to 33/312 (11%) patients showed MDS-PA at diagnosis, which were more frequently observed in the neutrophil lineage (6%), followed by monocytic (4%) and erythroid (4%) lineages. Four cases had multilineage MDS-PA. Afterwards, we investigated if the presence of MDS-PA was associated with underlying somatic mutations by performing targeted sequencing of 54 MDS/AML related genes (depth ≥500x) in 44 patients from the previous series (10 with MDS-PA and 34 without). Next generation sequencing was performed, at diagnosis and after HDT/ASCT in FACS sorted CD34+ hematopoietic stem cells (HSCs) and dysplastic cell lineages from patients with MDS-PA, as well as in HSC from cases without MDS-PA. CD138+ BM plasma cells (PCs) from both cohorts were also sequenced using the same panel. Six out of the 10 cases with MDS-PA showed somatic mutations. Namely, HSCs from one patient had two mutations in TET2 [allele fraction (AF): 18%, ≥ 26017x] one in CALR (AF: 14%, 1158x) and another in ASXL1 (AF: 7%, 1339x). None of these mutations were present in myeloid/erythroid cells. A second patient had NPM1 mutated in HSCs (AF: 7%, 12825x), which was absent in neutrophils. A third case had TET2 mutated in HSCs (AF: 16%, 1233x) as well as in dysplastic monocytes (AF: 27%, 16647x) and neutrophils (AF: 23%, 21719x). In the fourth case, a mutation in BCORL1 was noted in dysplastic erythroid cells (AF: 10%, 796x). The fifth patient had TET2 mutated in both HSCs and dysplastic monocytes (AF: 45%-63%; ≥21799x). The sixth case had PHF6 mutated in HSCs (AF: 8%; 800x). In none of the patients were the mutations found in HSCs and/or dysplastic lineages, present in PCs. Within the control cohort of the 34 patients without MDS-PA, only two of them displayed somatic mutations in HSCs; one case had DNMT3A mutated (AF: 26%, 1900x) and the other TET2 (AF: 13%, 3400x). After demonstrating a correlation between MDS-PA and MDS/AML-related somatic mutations, we sought to analyze the prognostic significance of such alterations in MM. Since the follow-up of the present series of 312 cases is relatively short, we focused on a large series of 965 patients with longer follow up (median of 6.5 years) enrolled in GEM clinical trials, and for which the presence of CD56+ aberrant monocytes could be readily investigated. Noteworthy, this particular MDS-PA was again observed in a similar frequency as noted above (n=63; 6.5%) and as compared to the overall MM population, patients with MDS-PA showed significantly higher age, lower hemoglobin values and higher BMPC infiltration at diagnosis. Furthermore, they experienced more frequently hematological toxicity including anemia and neutropenia during treatment. Most interestingly, as compared to the overall MM population, patients with MDS-PA had significantly inferior progression-free (medians of 24 vs 37 months; P=.006) and overall survival (medians of 47 vs 73 months; P=.01). In conclusion, we showed for the first time that a fraction of newly diagnosed MM patients harbors MDS/AML-related somatic mutations in HSCs and myeloid/erythroid lineages, and that such patients could be predicted through flow-based screening for MDS-PA. The presence of MDS-PA identifies a subset of patients that experience more frequently hematological toxicity and display inferior survival; accordingly, screening for MDS-PA could become an important biomarker to tailor treatment in MM. Disclosures Paiva: Celgene: Honoraria, Research Funding; Janssen: Honoraria; Takeda: Honoraria, Research Funding; Sanofi: Consultancy, Research Funding; EngMab: Research Funding; Amgen: Honoraria; Binding Site: Research Funding. Oriol:Amgen: Honoraria, Other: Expert board committee; Janssen: Honoraria, Other: Expert board committee. Mateos:Amgen: Honoraria; Takeda: Honoraria; Celgene: Honoraria; Janssen: Honoraria.

Abstract: Early intervention in smoldering multiple myeloma (SMM) requires optimal risk stratification to avoid under- and overtreatment. We hypothesized that replacing bone marrow (BM) plasma cells (PC) for circulating tumor cells (CTC), and adding immune biomarkers in peripheral blood (PB) for the identification of patients at risk of progression due to lost immune surveillance, could improve the International Myeloma Working Group 20/2/20 model. Experimental Design: We report the outcomes of 150 patients with SMM enrolled in the iMMunocell study, in which serial assessment of tumor and immune cells in PB was performed every 6 months for a period of 3 years since enrollment. Results: Patients with & gt;0.015% versus ≤0.015% CTCs at baseline had a median time-to-progression of 17 months versus not reached (HR, 4.9; P  & lt; 0.001). Presence of & gt;20% BM PCs had no prognostic value in a multivariate analysis that included serum free light-chain ratio & gt;20, & gt;2 g/dL M-protein, and & gt;0.015% CTCs. The 20/2/20 and 20/2/0.015 models yielded similar risk stratification (C-index of 0.76 and 0.78). The combination of the 20/2/0.015 model with an immune risk score based on the percentages of SLAN+ and SLAN− nonclassical monocytes, CD69+HLADR+ cytotoxic NK cells, and CD4+CXCR3+ stem central memory T cells, allowed patient’ stratification into low, intermediate-low, intermediate-high, and high-risk disease with 0%, 20%, 39%, and 73% rates of progression at 2 years. Conclusions: This study showed that CTCs outperform BM PCs for assessing tumor burden. Additional analysis in larger series are needed to define a consensus cutoff of CTCs for minimally invasive stratification of SMM.