Abstract: Background: Patients with RRMM receive multiple lines of therapy in their disease course and often become refractory to or are intolerant of newer approved therapies (eg, IMiDs, anti-CD38 monoclonal antibody [mAb] therapy, proteasome inhibitors [PIs] ), limiting effective treatment options (Kumar et al. Leukemia. 2017; 31:2443). Efficacy outcomes decrease with each line of therapy, showing a need for agents with novel mechanisms of action to improve treatment responses and survival outcomes (Gandhi et al. Leukemia. 2019;33:2266). Melphalan flufenamide (melflufen) is a first-in-class peptide-drug conjugate (PDC) that targets aminopeptidases and rapidly releases alkylating agents into tumor cells. In the phase 2 HORIZON study (OP-106; NCT02963493), melflufen plus dexamethasone demonstrated encouraging efficacy in heavily pretreated patients with RRMM refractory to pomalidomide and/or an anti-CD38 mAb (overall response rate [ORR], 29%; median progressi on-free survival [PFS], 4.2 months; median overall survival [OS] , 11.6 months) with a clinically manageable safety profile characterized primarily by hematologic adverse events (Richardson et al. EHA 2020. Abs. EP945). A contemporary representative control cohort is often used to indirectly compare outcomes of patients in clinical trials versus real-world data. The retrospective MAMMOTH study investigated the natural history and outcomes of patients with RRMM refractory to anti-CD38 mAb therapy after treatment with conventional agents (Gandhi et al. Leukemia. 2019;33:2266), providing a benchmark for the evolving state of the RRMM treatment landscape. Outcomes in clinical studies of novel agents in RRMM have been compared with MAMMOTH previously (Costa et al. ASH 2019. Abs. 3125), but not specifically in patients with RRMM refractory to anti-CD38 mAb therapy. To contextualize the clinical benefit of melflufen plus dexamethasone compared with conventional agents for patients with RRMM refractory to anti-CD38 mAb therapy, an analysis was conducted evaluating efficacy outcomes in HORIZON versus MAMMOTH. Methods: HORIZON patients with RRMM refractory to anti-CD38 mAb in the last line of therapy in the intention-to-treat population at final analysis (data cutoff date, 14 Jan 2020) were included in this analysis (N=63). Patients received melflufen 40 mg (intravenously on day 1 of each 28-day cycle) plus dexamethasone 40 mg weekly until disease progression or unacceptable toxicity. The MAMMOTH dataset included patients who progressed while on anti-CD38 mAb therapy (N=275) and were subsequently treated (N=249). ORR was assessed by the investigator per the International Myeloma Working Group criteria. PFS was defined as the time between the first dose of therapy and disease progression or death. OS was defined as the time from refractoriness to anti-CD38 mAb therapy to death from any cause in contrast to clinical studies in which OS is generally measured from first dose of subsequent therapy. Results: Patients in HORIZON and MAMMOTH had similar baseline median age and profile of daratumumab and isatuximab refractoriness (Table). Patients in HORIZON were more heavily pretreated than those in MAMMOTH (median number of prior therapies [range], 5 [2-10] versus 4 [1-16]). Patients in MAMMOTH were often treated with triplet therapy as first subsequent therapy after anti-CD38 mAb therapy failure (Table). ORR for HORIZON patients who failed last-line therapy with an anti-CD38 mAb (N=63) was 35% versus 31% for all anti-CD38 mAb therapy-refractory patients who received conventional agents in MAMMOTH. Median PFS was 4.6 months (95% CI, 3.7-6.4) versus 3.4 months (95% CI, 2.8-4.0), and median OS from last line was 15.4 months (95% CI, 12.0-25.6) versus 9.3 months (95% CI, 8.1-10.6) for these patients in HORIZON and MAMMOTH, respectively. Conclusion: This indirect comparison of patients with RRMM refractory to anti-CD38 mAb therapy in HORIZON and MAMMOTH suggests longer survival outcomes with melflufen plus dexamethasone (median PFS and OS of 4.6 and 15.4 months, respectively) versus those with conventional agents, despite HORIZON having more heavily pretreated patients. This analysis underscores the high burden of disease and unmet needs for patients with RRMM and the feasibility of novel combination therapy in this setting. Disclosures Blade Creixenti: Takeda: Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees. Mateos:Roche: 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; 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; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Honoraria; Regeneron: 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; Sanofi: 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; Oncopeptides: 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. Oriol:GlaxoSmithKline: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy; Amgen: Consultancy, Speakers Bureau; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Larocca:GSK: Honoraria; Takeda: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; 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. Cavo:Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel accomodations, Speakers Bureau; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel accomodations, Speakers Bureau; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; GlaxoSmithKline: Honoraria, Speakers Bureau; Karyopharm: Honoraria; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Rodríguez-Otero:Janssen: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Abbvie: Consultancy; Kite: Consultancy; Sanofi: Consultancy; Celgene/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); Medscape: Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria; GlaxoSmithKline: Consultancy, Current Employment, Current equity holder in publicly-traded company; Oncopeptides: Consultancy. Leleu:GSK: Honoraria; Sanofi: Honoraria; Novartis: Honoraria; Carsgen: Honoraria; Incyte: Honoraria; Merck: Honoraria; Amgen: Honoraria; Karyopharm: Honoraria; AbbVie: Honoraria; BMS-celgene: Honoraria; Janssen: Honoraria; Oncopeptide: Honoraria. Nadeem:Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Adaptive: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Sanofi: Consultancy, 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, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Janssen: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES. Hassoun:Novartis: Consultancy; Celgene: Research Funding; Takeda: Research Funding. Touzeau:Abbvie: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses, Research Funding; Amgen: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; GlaxoSmithKline: Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; Sanofi: Honoraria, Research Funding. Amor:Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Celgene-BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; GSK: Membership on an entity's Board of Directors or advisory committees. Maisel:Takeda: Honoraria, Speakers Bureau; Incyte: Honoraria, Speakers Bureau; Kite: Honoraria, Speakers Bureau; Texas Oncology: Current Employment; Karyopharm: Honoraria, Speakers Bureau; Incyte: Honoraria, Speakers Bureau; Takeda: Honoraria, Speakers Bureau; Karyopharm: Honoraria, Speakers Bureau; Texas Oncology: Current Employment; Celgene: Honoraria, Speakers Bureau; Janssen: Honoraria, Speakers Bureau; Kite: Honoraria, Speakers Bureau; Amgen: Honoraria, Speakers Bureau; Amgen: Honoraria, Speakers Bureau; Celgene: Honoraria, Speakers Bureau; Janssen: Honoraria, Speakers Bureau. Mazumder:The Oncology Institute: Current Employment; Amgen: Honoraria, Speakers Bureau; Celgene: Honoraria, Speakers Bureau; Takeda: Honoraria, Speakers Bureau. Raptis:INTEGRA: Consultancy, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; UPMC: Current Employment. Puig:BRISTOL-MYERS SQUIBB: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding, Speakers Bureau; AMGEN: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding; CELGENE: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding, Speakers Bureau; JANSSEN: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding; TAKEDA: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding; THE BINDING SITE: Consultancy, Honoraria. Zavisic:Oncopeptides AB: Current Employment, Current equity holder in publicly-traded company. Thuresson:Oncopeptides: Consultancy, Current equity holder in publicly-traded company; Statisticon: Current Employment. Harmenberg:Oncopeptides AB: Consultancy, Current equity holder in publicly-traded company, Divested equity in a private or publicly-traded company in the past 24 months, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Medivir AB: Current equity holder in publicly-traded company; Ultupharma AB: Current equity holder in private company. Richardson:Celgene/BMS, Oncopeptides, Takeda, Karyopharm: Research Funding. OffLabel Disclosure: This is an indirect comparison of clinical studies, including a phase 2 investigational study of melflufen in RRMM

Abstract: Continuous treatment with lenalidomide (R) and dexamethasone (d) is a standard of care for multiple myeloma (MM) patients (pts) not candidates for autologous stem cell transplantation (ASCT). As previously reported, the addition of Clarithromycin (C) to Rd has proven to be safe and effective, and case-control analyses suggested a significant additive value with the combination. C optimizes the therapeutic effect of glucocorticoids by increasing the area under the curve, has immunomodulatory effects and may have direct antineoplastic properties. However, there are not randomized phase III trials confirming these results. GEM-Claridex in an open, randomized, phase III trial for untreated newly diagnosed MM pts ineligible for ASCT. Enrolled pts were randomly assigned 1:1 to receive 28-day cycles of R (25mg po qd days 1-21), d (40mg po [20mg in pts & gt;75 years], days 1, 8, 15 and 22) plus or minus C (500mg po bid) until disease progression or unacceptable toxicity. The primary endpoint was progression-free survival (PFS). Secondary endpoints included overall response rate (ORR), overall survival (OS) and minimal residual disease (MRD) negativity rate and safety. MRD was evaluated in 99 pts using Euroflow NGF (limit of detection, 2x10-6). As expected, most pts in CR were tested for MRD whereas the majority of pts with missing MRD data achieved VGPR or less and were thus considered as MRD-positive for intent to treat analyses. Two hundred and eighty-eight pts were included (144 to C-Rd and 144 to Rd). Median age was 76 (range: 65-93), 36.8% of pts had ISS 3 and 15.6% presented with high-risk cytogenetic abnormalities. Key baseline characteristics were well balanced between the two arms. The addition of C to Rd resulted in deeper responses with a ≥ complete response (CR) rate of 20.1% in the C-Rd arm compared to 11.2% in the Rd arm (p = 0.037). Also, the ≥ very good partial response (VGPR) rate was 52.8% in the C-Rd arm as compared to the 37.1% in the Rd arm (p = 0.007). MRD analysis was performed at suspected CR and yearly afterwards. On intent-to-treat, 5/144 (3,5%) and 9/143 (6,2%) of pts achieved undetectable MRD with C-Rd and Rd, respectively (p = 0,7). With a median follow-up of 16 months (range, 1-47), no significant differences were observed in PFS: in the C-Rd arm the median was 23 months and has not been reached in the Rd arm (p = 0.09); furthermore, although disease progression and/or death rate was comparable in both arms (C-Rd: 57/144 [39.6%] vs Rd: 45/144 [31.2%] ), a trend towards shorter PFS was observed in the C-Rd group (Figure 1). This effect was less evident in younger ( & lt;75) pts (median PFS, C-Rd: 24 months vs Rd NR, p = 0,588) but, in older pts (≥ 75), the addition of C to Rd resulted into a significant deleterious effect on PFS (median PFS, C-Rd: 19 vs Rd 28 months, p = 0.03) (Figure 2a and 2b). Irrespectively of treatment arm, pts with MRD negative had significantly longer PFS (NR vs 26 months, p = 0,03). Concerning OS, no differences have been identified (p = 0.41), although median has not been reached yet in any arm. Out of the 33 and 28 deaths documented in the C-Rd and Rd arms respectively, the percentage of pts dying w/o documented PD was significantly higher in the C-Rd group (27/33 [82%] vs 13/27 [48%] , p = 0.004). Furthermore, in the C-Rd arm, the most frequent causes of death were severe infections (14/27 [52%] and cardiovascular events 6/27 [22%] ) the majority of them occurring in older (≥75) pts (20/27, 74%). The most common G3-4 adverse events (AE) in the C-Rd and Rd arms were hematologic (neutropenia: 10,4% vs 16,7% [p = ns] and anemia: 2,1% vs 6,9% [p = 0,04] , respectively). G3-4 infections occurred in 16% of cases in both arms and were the most frequent non-hematological AE. 7% of pts in both arms developed G3-4 GI toxicity and there were no differences between the two arms in G3-4 skin-related AEs (2,8% vs 3,5%). Only one case of invasive SPM (colon cancer) in the C-Rd arm was reported. In conclusion, the addition of C to Rd in transplant ineligible newly diagnosed MM pts significantly increases the rate and depth of responses but it is not associated with an improved PFS and OS due to a higher proportion of deaths in the C-Rd arm, mostly infectious, in pts & gt; 75 years and being early deaths. Overexposure to steroids due to the delayed clearance induced by C in this elderly population could explain our results. Figure Disclosures Puig: The Binding Site: Honoraria; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Takeda: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Research Funding. Rosinol Dachs:Janssen, Celgene, Amgen and Takeda: Honoraria. De Arriba:Celgene: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Takeda: Honoraria. Oriol:Celgene Corporation: Consultancy, Speakers Bureau; Takeda: Consultancy, Speakers Bureau; Janssen: Consultancy; Amgen: Consultancy, Speakers Bureau. De La Rubia:AbbVie: Consultancy; AMGEN: Consultancy; Celgene Corporation: Consultancy; Takeda: Consultancy; Janssen: Consultancy. Amor:Celgene: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees. Martín Sánchez:GILEAD SCIENCES: Research Funding. Rossi:BMS: Research Funding; Janssen, Celgene, Amgen: Consultancy. Coleman:Merck: Research Funding; Pharmacyclics: Speakers Bureau; Kite Pharmaceuticals: Equity Ownership; Gilead, Bayer, Celgene: Consultancy, Research Funding, Speakers Bureau. 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. San-Miguel:Amgen, Bristol-Myers Squibb, Celgene, Janssen, MSD, Novartis, Roche, Sanofi, and Takeda: Consultancy, Honoraria. Bladé:Jansen, Celgene, Takeda, Amgen and Oncopeptides: Honoraria. Niesvizky:Takeda, Amgen, BMS, Janssen, Celgene: Consultancy, Research Funding. Mateos:EDO: Membership on an entity's Board of Directors or advisory committees; Pharmamar: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; 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; 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; Adaptive: Honoraria.

Abstract: Abstract 334 Introduction: The Spanish Myeloma Group (PETHEMA/GEM) conducted a randomized phase III trial comparing induction with thalidomide/dexamethasone (TD) vs. bortezomib/thalidomide/dexamethasone (VTD) vs. VBMCP/VBAD/Bortezomib (VBMCP/VBAD/B) in patients 65 years-old or younger with newly diagnosed symptomatic MM and ASCT with MEL-200 followed by maintenance with thalidomide/bortezomib (TV) vs. thalidomide (T) vs. alfa-2b-interferon (alfa2-IFN). The induction part of the study has been recently published and the maintenance results are reported here. End-points: The primary end-point was progression-free survival (PFS) and the secondary end-points were increase of response rate, overall survival (OS) and safety. Patients and Methods: The maintenance treatment consisted of TV (thalidomide 100 mg daily plus one cycle of bortezomib at 1.3 mg/m2 on days 1, 4, 8 and 11 every 3 months) versus T (single agent thalidomide at a dose of 100 mg daily) versus alfa2-IFN (subcutaneous alfa2b-IFN at a dose of 3 MU three times per week). The planned maintenance duration was three years or until disease progression or toxicity. From February 1, 2007 to January 27, 2011 266 patients were randomized to maintenance therapy (TV: 89; T: 87, alfa2-IFN: 90). Response and survival were evaluated on an intention-to-treat basis. Responses, relapses and progressions (EBMT criteria) were monitored by an external contract research organization and centrally reassessed. Results: Patient's characteristics at diagnosis such as age, M-protein type, ISS stage, cytogenetics and presence of extramedullary plasmacytomas as well as induction regimen (VTD, TD and VBMCP/VBAD/Bortezomib) and diagnosis-randomization interval were similarly distributed among the 3 arms. The response status at the time of randomization for maintenance after ASCT was CR: 51%, nCR: 12%, PR: 34%, MR 2% and SD: 1% and was well balanced in the three groups. The CR rate with maintenance was improved by 19% with TV, 15% with T and 17% with alfa2-IFN (p=NS). After a median follow-up of 34.9 months, the PFS was significantly longer with TV compared with T and alfa2-IFN (figure 1, p=0.0009). However, OS was not significantly different among the 3 arms. Grade 3 and 4 hematological toxicity was similar (22.2% vs. 16% vs. 21.8%). No peripheral neuropathy (PN) was observed with alfa2-IFN being its frequency similar with TV (12.2%) and T (10.1%). No grade IV PN was observed. Dose reductions for TV, T and alfa2-IFN were required in 33.3%, 33.7% and 19.5% of the patients, respectively. The discontinuation rate due to progressions was not significantly diferent among the three arms (35% vs 24% vs 20%, p=NS). The discontinuation rate due to toxicity was higher with thalidomide compared with TV (30.3% vs. 15.6%, p= 0.08) and with alfa2-IFN (30.3% vs. 18.3%, p=0.17). Patients with high-risk cytogenetics [t(4;14), t(14;16) and/or del 17p] had a trend towards a shorter PFS (p=0.1) and a significantly shorter OS (p=0.03). The incorporation of bortezomib was not able to overcome the poor impact of high-risk cytogenetics. Conclusion: The addition of bortezomib to thalidomide maintenance resulted in a significantly longer PFS when compared with thalidomide alone or with single agent alfa2-IFN with no increased toxicity. However, the addition of bortezomib did not overcome the poor impact of high-risk cytogenetics. Disclosures: Rosiñol: Janssen, Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees. Oriol:Janssen: Honoraria; Celgene: Honoraria. De La Rubia:Celgene, Janssen: Consultancy, Speakers Bureau. Granell:Janssen: Honoraria; Celgene: Honoraria. de Arriba:Jansen: Honoraria; Celgene: Honoraria. Alegre:Janssen: Honoraria; Celgene: Honoraria. Cibeira:Janssen: Honoraria; Celgene: Honoraria. Mateos:Janssen: Honoraria; Celgene: Honoraria. Lahuerta:Janssen: Honoraria; Celgene: Honoraria. San Miguel:Janssen: Honoraria; Celgene: Honoraria; Onix: Honoraria; Novartis: Honoraria. Bladé:Janssen: Honoraria; Celgene: Honoraria; Novartis: 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: Introduction: The GEM-CESAR trial is a potentially curative strategy for high-risk smoldering multiple myeloma (HRsMM) patients in which the primary endpoint is the assessment of bone marrow minimal residual disease negativity by next generation flow (NGF). However, alternative methods of tumor burden evaluation in serum, like Quantitative Immunoprecipitation Mass Spectrometry (QIP-MS), a polyclonal antibody-based technology to identify intact immunoglobulins, have been also evaluated. Patients and Methods: Ninety HRsMM patients included in the GEM-CESAR trial received six 4-weeks cycles of carfilzomib, lenalidomide and dexamethasone followed by high dose melphalan and ASCT and 2 further cycles of consolidation with the same regimen. All patients received maintenance with lenalidomide up to 2 years. SPEP and IFE were performed using standard procedures and MRD was analyzed by flow cytometry following EuroFlow recommendations. QIP-MS assessment has been previously described (1) and allowed us the characterization of the isotype of each Ig trough immunoprecipitation with paramagnetic beads as well as the measurement of the molecular mass of each Ig for each specific patient, with enough precision and accuracy to establish clonality. Standard response assignment was carried out as per the IMWG guidelines. Results: First, we confirmed the higher sensitivity of QIP-MS to identify the presence of a serum M-spike as compared to conventional protein immunofixation electrophoresis methods. Amongst patients in CR, QIP-MS identified the M-spike in 18/30 (60%) post-induction, 18/47(38%) post-ASCT and 25/58(43%) post-consolidation. Interestingly, similar results were obtained with MRD-NGF post-induction [17/30(57%)] and post-ASCT [15/47(32%)] although the positive rate post-consolidation [15/58(26%)] was higher with QIP-MS. Then, we analyzed the overall concordance between the results obtained with QIP-MS and MRD-NGF at the three timepoints of disease evaluation, finding an overall concordance of 81% post-induction (n=76), 70% post-transplant (n=76) and 68% post-consolidation (n=77). Thus, when compared to the results of MRD-NGF, QIP-MS demonstrated sensitivities of 100%, 79% and 77% post-induction, post-ASCT and post-consolidation, and negative predictive values (NPV) of 100%, 79% and 82% at each respective time-point. (P & lt; 0,0001; P = 0,0004; P = =,0012) Evaluation of discrepant cases showed 14 out of 22 MRD-NGF-negative patients post-induction for whom QIP-MS identified a M-spike; in some cases (i.e. IgG MM isotype) this may be related to a longer immunoglobulin half-life. There were no cases with detectable disease by NGF but QIP-MS negative. By contrast, post-ASCT, QIP-MS was negative in seven MRD-positive patients, two of whom became MRD-NGF-negative after consolidation; at last follow-up, none of them have progressed. On the other hand, sixteen patients with negative MRD-NGF after ASCT had a detectable M-spike by mass spectrometry. Of note, the M-spike became undetectable after consolidation in six out of these 16 patients. Post-consolidation, there were 7 patients in which MRD-NGF was positive but QIP-MS negative: MRD evaluation during maintenance is pending but none of them have so far progressed. By contrast, there were 18 patients with the M-spike detectable by QIP-MS but MRD-NGF negative: follow-up of these patients will address their outcome but, the only patient that has progressed so far had MRD-NGF negative post-induction, becoming positive post-transplant and consolidation, but the M-spike was detectable by QIP-MS throughout. Conclusions: M-spike monitoring by QIP-MS shows a moderate concordance with the MRD assessment by NGF in this group of HRsMM homogeneously treated. Longer follow-up will allow us to unravel the outcome of discordant cases and to define the specificity of QIP-MS and its complementary value to NGF. North S, Barnidge D, Brusseau S, Patel R, Haselton M, Du Chateau B, et al. QIP-MS: A specific, sensitive, accurate, and quantitative alternative to electrophoresis that can identify endogenous m-proteins and distinguish them from therapeutic monoclonal antibodies in patients being treated for multiple myeloma. Clinica Chimica Acta 2019;493:S433. Disclosures Puig: Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Janssen: Consultancy, Honoraria, Research Funding; The Binding Site: Honoraria; Takeda, Amgen: Consultancy, Honoraria. Mateos:Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive: Honoraria; GSK: Membership on an entity's Board of Directors or advisory committees; Pharmamar: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; 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; EDO: Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees. 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. Rodriguez Otero:Takeda: Consultancy; Kite Pharma: Consultancy; BMS: Honoraria; Celgene Corporation: Consultancy, Honoraria, Speakers Bureau; Janssen: Consultancy, Honoraria. Oriol:Celgene, Amgen, Takeda, Jansse: Consultancy, Speakers Bureau. Rios: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. Alegre:Celgene, Amgen, Janssen, Takeda: Membership on an entity's Board of Directors or advisory committees. de la Rubia:AbbVie: Consultancy; Janssen: Consultancy; Amgen: Consultancy; Celgene: Consultancy; Takeda: Consultancy. De Arriba:Amgen: Consultancy, Honoraria; Takeda: Honoraria; Janssen: Consultancy, Honoraria; Celgene: Consultancy, Honoraria. Ocio:Mundipharma: Research Funding; Pharmamar: Consultancy; Amgen: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria; AbbVie: Consultancy; Takeda: Consultancy, Honoraria; Array Pharmaceuticals: Research Funding; Sanofi: Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Seattle Genetics: Consultancy; Novartis: Consultancy, Honoraria; BMS: Honoraria. Bladé:Janssen, Celgene, Amgen, Takeda: Membership on an entity's Board of Directors or advisory committees; Irctures: Honoraria. Lahuerta:Takeda, Amgen, Celgene and Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Abstract: Abstract 3949 Although in MM an optimal response to front-line therapy is a surrogate for extended survival, two class of patients fall outside this paradigm: those that after treatment show unsustained complete remission (CR) and those that not achieving CR, return into an MGUS-like signature and experience nevertheless long term disease control (LTDC). The prospective identification of the later group remains to be accomplished. Herein, we hypothesized that whole BM immunophenotypic profiling by multiparameter flow cytometry (MFC) would help to identify upfront, symptomatic MM patients with an occult MGUS-like signature (from here on named MGUS-like-MM). For this purpose, the relative frequency of plasma cells (plus the balance between clonal and normal PC), precursor and mature B-cells, T- and NK-cells, erythroblasts, monocytes, neutrophils and eosinophils was determined in 698 newly diagnosed, transplant eligible MM patients included in two consecutive GEM/PETHEMA trials: GEM2000 (VBMCP/VBAD; n=486) and GEM2005 〈 65y (randomized induction with the same chemotherapy plus bortezomib in the last two cycles or thalidomide/dexamethasone or bortezomib/thalidomide/dexamethasone followed by HDT/ASCT; n=212). In addition, we extended this analysis to 114 high-risk smoldering MM patients included in the Quiredex trial. Median follow-up was 63 months for symptomatic MM patients. Unsupervised hierarchical cluster analysis was used on the log2 transformed values of the 11 variables described above. Whole BM immunophenotypic profiling identified a cluster of 176 (25%) symptomatic MM patients “assigned as MGUS-like-MM” based on the following phenotypic features: significantly decreased median numbers of myelomatous PC together with a significant increment of eosinophils, neutrophils, monocytes, T- and NK -cells, mature B-cells and particularly normal PC. This subgroup was characterized by a favorable clinical presentation with increased (P 〈 .005) frequency of ISS stage I or II (88%), high baseline hemoglobin (116 g/L) and albumin (3.8 g/dL) values. MGUS-like-MM patients showed an increased frequency of hyperdiploid DNA content (63%; P=.001) and a lower incidence of t(4;14) (3%; P=.05). When compared to the overall population, MGUS-like-MM patients showed a markedly superior median TTP (88 vs 40 months; P 〈 .001) and OS (141 vs 61 months; P 〈 .001). Moreover, the MGUS-like signature was a strong predictor for LTDC, with 16% of these patients being disease-free at 10 years as compared to 3.5% in the overall MM population (P 〈 .001). Interestingly, while the depth of response achieved after HDT/ASCT translated into superior TTP (P=.032) and OS (P=.005) in the overall population, MGUS-like-MM patients failing to achieve CR showed non significantly different median TTP (80m vs 105m; P=.167) and OS (not reached vs 141m; P=.438) as compared to those attaining CR, respectively. Finally, it should be pointed out that this MGUS-like signature was not restricted to symptomatic MM, since we have also found a subset of high-risk smoldering MM patients with the same signature. These later patients showed a significantly lower risk of progression into symptomatic MM as compared to the rest of high-risk smoldering MM patients (data not shown). In summary, whole BM immunophenotypic profiling by MFC is capable to identify a subset of symptomatic MM patients with an occult MGUS-like signature associated with prolonged survival. Given that in this subgroup of patients the value of CR is not as important as in the rest of MM patients, the prospective identification of this signature may contribute to discriminate a sub-optimal response that require additional treatment from a residual “MGUS-like component” that may remain stable without further treatment. Disclosures: Paiva: Celgene: Honoraria; Miellenium: Honoraria; Janssen: Honoraria. Martínez-López:Celgene: Honoraria. Mateos:Celgene: Honoraria; Miellenium: Honoraria; Janssen: Honoraria. De La Rubia:Celgene, Janssen: Consultancy, Speakers Bureau. Lahuerta:Celgene: Honoraria; Millenium: Honoraria. Blade:Celgene: Honoraria; Millenium: Honoraria; Janssen: Honoraria. San Miguel:Celgene: Honoraria; Millenium: Honoraria; Janssen: Honoraria.

Abstract: Background: Recent advances have improved survival in multiple myeloma (MM; Kumar et al. Leukemia. 2014); however, the disease remains incurable. Patients with triple-class refractory MM have a median overall survival (OS) of only 9.2 months (Ghandi et al. Leukemia. 2019). These patients and those with poor-risk features, such as high-risk cytogenetics, have few treatment options and represent a patient group with a very poor prognosis and high unmet medical need. Melflufen is a lipophilic peptide-conjugated alkylator that rapidly delivers a highly cytotoxic payload into myeloma cells through peptidase activity. Meflufen is taken up by myeloma cells and immediately cleaved by peptidases into hydrophilic alkylator payloads that induce irreversible DNA damage and apoptosis. This updated analysis of the ongoing HORIZON study in patients with MM refractory to pomalidomide (pom) and/or daratumumab (dara) includes a subgroup analysis of patients with triple-class refractory (no response or progression on or within 60 days of last dose to at least 1 IMiD, 1 proteasome inhibitor [PI], and 1 anti-CD38 monoclonal antibody) and high-risk cytogenetics at baseline (NCT02963493). Methods: Patients with relapsed refractory MM (RRMM) must have received ≥2 prior lines, been exposed to an IMiD and PI, and be refractory to pom and/or dara. Patients receive 40-mg melflufen intravenously on day 1 of each 28-day cycle and 40-mg weekly dexamethasone (dex; 20 mg for patients aged ≥75 years) until progressive disease (PD) or unacceptable toxicity. The primary endpoint is overall response rate (ORR; ≥ partial response [PR]; investigator assessed per International Myeloma Working Group criteria). Secondary endpoints include safety, clinical benefit rate (CBR; ≥ minimal response), progression-free survival (PFS), OS, and duration of response (DOR). Results: As of 6 May 2019, 121 patients were treated. The median age was 64 years (range, 35-86), median time since diagnosis was 6.2 years (range, 0.7-25), 29% of patients had International Staging System stage 3 disease, and 62% with available cytogenetic data (n=81) had high-risk cytogenetics at study entry. The median number of prior lines was 5 (2-12). All patients were pom or dara refractory and received prior PIs and IMiDs; 74% were triple-class refractory. With a median follow-up of 10.8 months, 29% of patients were on ongoing treatment. Of 86 patients (71%) who discontinued treatment, 69% discontinued due to PD, 20% due to adverse events (AEs), and 12% for other reasons. In total, 113 patients had available response data. ORR was 28%; 1 patient achieved stringent complete response (sCR), 9% very good PR (VGPR), and 19% PR. CBR was 40%. Median PFS for all patients treated (N=121) was 4.0 months (95% CI, 3.7-4.6), median OS was 11.2 months (95% CI, 8.1-13.9), and median DOR was 4.4 months (95% CI, 3.6-8.3). Efficacy was examined in poor-risk patient subsets with available response data. ORR was 20% in patients with triple-class refractory disease (n=83). ORR in patients with high-risk cytogenetics was 28%. Median DOR was 3.6 months in responders with triple-class refractory disease. DOR in patients with high-risk cytogenetics was 5.1 months. Treatment-related grade 3 and grade 4 AEs were reported in 24% and 49% of patients, respectively. Most common (≥5%) grade 4 AEs were thrombocytopenia (36%) and neutropenia (31%). The incidence of treatment-related grade 3/4 nonhematologic AEs was low; most commonly pneumonia (3%), fatigue (2%), and upper respiratory tract infection (2%). Treatment-related serious AEs occurred in 20% of patients. No treatment-related deaths were reported. Conclusion: Melflufen continues to show promising activity (ORR, 28%) in patients with late-stage RRMM refractory to dara and/or pom and was generally well tolerated, with infrequent nonhematologic AEs and, of the 121 patients treated, 14% discontinued due to AEs. Additionally, melflufen has comparable efficacy in subsets of patients with poor-risk features, including triple-class refractory and high-risk cytogenetics, relative to the overall HORIZON patient population. Melflufen plus dex is being further investigated vs pom plus dex in the OCEAN phase 3 study (OP-103; NCT03151811) in patients with RRMM refractory to lenalidomide. Disclosures Mateos: Amgen: 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; 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; GSK: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; EDO: Membership on an entity's Board of Directors or advisory committees; Pharmamar: Membership on an entity's Board of Directors or advisory committees. Oriol:Janssen: Consultancy; Takeda: Consultancy, Speakers Bureau; Celgene Corporation: Consultancy, Speakers Bureau; Amgen: Consultancy, Speakers Bureau. Larocca:Amgen: Honoraria; Takeda: Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Rodriguez Otero:Kite Pharma: Consultancy; BMS: Honoraria; Celgene Corporation: Consultancy, Honoraria, Speakers Bureau; Takeda: Consultancy; Janssen: Consultancy, Honoraria. Bladé:Jansen, Celgene, Takeda, Amgen and Oncopeptides: Honoraria. Cavo:AbbVie: 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, Other: travel accommodations, Speakers Bureau; janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accommodations, Speakers Bureau; novartis: Honoraria; takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; bms: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Hassoun:Celgene: Research Funding; Janssen: Research Funding; Novartis: Consultancy. Leleu:Sanofi: Honoraria; Oncopeptide: Honoraria; Takeda: Honoraria; Karyopharm: Honoraria; Amgen: Honoraria; Carsgen: Honoraria; Incyte: Honoraria; Novartis: Honoraria; Celgene: Honoraria; Janssen: Honoraria; BMS: Honoraria; Merck: Honoraria. Amor:Takeda: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees. Maisel:Texas Oncology: Employment; Amgen: Honoraria, Speakers Bureau; Celgene: Honoraria, Speakers Bureau; Takeda: Honoraria, Speakers Bureau; Incyte: Honoraria, Speakers Bureau; Janssen: Honoraria, Speakers Bureau; Gilead: Honoraria, Speakers Bureau; Verastem: Honoraria, Speakers Bureau. Paner:Amgen: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Cellectar: Consultancy, Honoraria; Dova: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Oncopeptides: Consultancy, Honoraria; Rush University Medical Center: Employment; Cellectar: Consultancy, Honoraria; Janssen: Consultancy, Honoraria. Harmenberg:Oncopeptides: Consultancy, Equity Ownership. Byrne:Oncopeptides: Consultancy; Takeda: Consultancy. Thuresson:Oncopeptides: Employment, Equity Ownership. Zubair:Oncopeptides: Employment, Equity Ownership. Richardson:Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol-Myers Squibb: Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi: Membership on an entity's Board of Directors or advisory committees; Karyopharm: Membership on an entity's Board of Directors or advisory committees. OffLabel Disclosure: This is a phase 2 investigational study of melflufen in RRMM

Abstract: 8048 Background: Melphalan flufenamide (melflufen) is a first-in-class peptide-drug conjugate (PDC) that leverages aminopeptidases and rapidly releases alkylating agents inside tumor cells. Melflufen has a mechanism of action distinct from other alkylating agents (Slipicevic et al. AACR 2020. Abs. 1843). In the O-12-M1 (NCT01897714) and HORIZON (OP-106; NCT02963493) studies, melflufen plus dex showed meaningful efficacy and a clinically manageable safety profile in pts with RRMM (Richardson et al. Lancet Haematol. 2020;7:5; Richardson et al. J Clin Oncol. 2020;Dec 9 [Epub]). This pooled analysis examines pts from these studies exposed to prior alkylators. Methods: Both the O-12-M1 and HORIZON studies included pts with RRMM who received ≥ 2 prior lines of therapy (LoTs) and had a primary endpoint of overall response rate (ORR). Secondary endpoints included progression-free survival (PFS) and safety. Data from the 2 studies were pooled and analyzed according to previous exposure and refractoriness to alkylators before study entry. Refractoriness to prior alkylator therapy was defined as disease that failed to achieve a minimal response or progressed while on therapy, or within 60 d of last therapy. Results: Of 202 pts (HORIZON: n = 157, cutoff January 14, 2020; O-12-M1: n = 45, cutoff October 29, 2019), 178 (88%) had been exposed to alkylators in ≥ 1 prior LoT (see Table for subgroups). Pts exposed and refractory to alkylators in ≥ 2 LoTs had the highest number of pts refractory to an alkylator in the last LoT (61%), and 82% were refractory to an alkylator within 12 mo of study entry. Meaningful response rates were seen in all subgroups, except for pts who were exposed and refractory to alkylators in ≥ 2 prior LoTs (see Table). PFS trended toward being shorter with higher exposure and refractoriness to prior alkylators. Results should be interpreted with caution due to limited pt numbers. Grade 3/4 adverse events (AEs) were similar between pts exposed to prior alkylators (O-12-M1: 85%; HORIZON: 89%) and the overall population (O-12-M1: 84%; HORIZON: 89%). The most common AEs were hematologic, but were mostly reversible and clinically manageable. Nonhematologic AEs were infrequent and primarily grade 1/2. Conclusions: Melflufen in combination with dex showed meaningful efficacy and a clinically manageable safety profile in pts with RRMM exposed/refractory to prior alkylators. Clinical trial information: NCT02963493 and NCT01897714. [Table: see text]

Abstract: Background: The randomized PETHEMA/GEM phase III trial GEM05menos65 (www.clinicaltrials.gov NCT00461747) demonstrated that pretransplant induction therapy with VTD resulted in a significantly higher CR rate both, pretransplant and postransplant and in a significantly longer progression-free survival (PFS) when compared with thalidomide/dexamethasone (TD) and combination chemotherapy plus bortezomib (VBMCP/VBAD/B) (Rosiñol et al, Blood 2012). We report here the long-term results of the trial, five years after the last patient was included. Methods: From April 6, 2006 to August 5, 2009, 386 patients younger than 65 years with newly diagnosed symptomatic multiple myeloma (MM) were randomized to receive three different induction regimens: six 4-week cycles of TD (thalidomide 200 mg daily; dexamethasone 40 mg on days 1-4 and 9-12) vs. six 4-week cycles of VTD (TD at identical doses plus i.v. bortezomib 1.3 mg/m2 on days 1, 4, 8 and 11) vs. combination chemotherapy plus bortezomib (4 cycles of alternating VBMCP and VBAD chemotherapy followed by two cycles of i.v. bortezomib at the usual dose of 1.3 mg/m2 on days 1,4,8,11 every 3 weeks). The duration of the induction therapy was 24 weeks in all arms. All patients were planned to undergo ASCT with high-dose melphalan at 200 mg/m2 followed by maintenance therapy with thalidomide/bortezomib (TV) vs. thalidomide (T) vs. alfa-2b-interferon (alfa2-IFN) for 3 years. One-hundred and thirty patients were allocated to VTD, 127 to TD and 129 to VBMCP/VBAD/B. Seventy out of the 330 patients (21%) with cytogenetic studies had high-risk cytogenetics [t(4;14), t(14;16) and/or 17p deletion]. Patient characteristics at diagnosis and prognostic factors such as ISS, cytogenetics and maintenance arm were similarly distributed in the 3 arms. Results: After a median follow-up of 70.6 months, VTD resulted in a significantly longer PFS when compared with TD and VBMCP/VBAD/B (56.1 vs 29.2 vs 39.9 months, p=0.005) (Figure 1). The estimated overall survival (OS) at 8 years was 60% with no significant differences among the 3 arms. In the overall series, the PFS was significantly shorter in patients with high-risk cytogenetics compared with patients with standard-risk (15.7 vs. 44.3 months, p=0.003). In the TD and in the VBMCP/VBAD/B arm patients with high-risk cytogenetics had a significantly shorter PFS than patients with standard-risk (8.9 vs 32.8 months, p=0.04 in TD group; 14.1 vs. 43.3 months, p=0.05 in VBMCP/VBAD/B group). However, there was no significant difference in the VTD arm (23.6 vs 56.1 months, p=0.2). Patients with high-risk cytogenetics had a significantly shorter OS in the overall series (median 42.1 months vs not reached, p=0.00001) and this was observed in the three treatment arms: VTD median 37.1 months vs not reached (p=0.001), TD median 54.2 months vs not reached (p=0.06), VBMCP/VBAD/B median 30.2 months vs not reached (p=0.007). The achievement of a deeper response at the end of induction was associated with a longer PFS and OS. Thus, patients achieving CR at the end of induction had a significantly longer PFS than patients achieving a lower degree of response (median 62 vs. 28 months, p=0.00001), irrespective of the treatment arm. Furthermore, on an intention to treat basis, patients who were in postrasplant CR had a significantly longer PFS (p 〈 0.00001) and OS (p 〈 0.00001) than those who did not reach CR after ASCT (p 〈 0.001). In the overall series the OS after progression was 30.5 months and was not significantly different among the 3 arms (VTD 25.4 months, TD 50 months, VBMCP/VBAD/B 30.2 months, p=0.4). Patients with high-risk cytogenetics had a significantly shorter OS after relapse in the overall series (13.3 months vs. 37.5 months, p=0.001), in the VTD arm (13.3 vs 33.9, p=0.01) and in the VBMCP/VBAD/B arm (8.5 vs 38 months, p=0.01). Conclusions: Our long-term results confirm that induction with VTD results in a significantly longer PFS when compared with TD and VBMCP/VBAD/B. Patients with high-risk cytogenetics had a worse outcome even with the use of novel drugs. Finally, the PFS of 56 months achieved with VTD is the longest ever reported in the first line treatment of younger patients with MM elegible for ASCT and support the use of VTD as the standard of care for pretransplant induction therapy. Figure 1: PFS according to the induction arm Figure 1:. PFS according to the induction arm Disclosures Rosiñol: Janssen: Honoraria; Celgene: Honoraria. Oriol:Celgene Corporation: Consultancy. De La Rubia:Janssen: Honoraria; Celgene: Honoraria. Gutierrez:Janssen: Honoraria; Celgene: Honoraria. Martinez-Lopez:Janssen: Honoraria; Celgene: Honoraria. Alegre:Janssen: Honoraria; Celgene: Honoraria. Lahuerta:Janssen: Honoraria; Celgene: Honoraria. San Miguel:Janssen: Honoraria; Celgene: Honoraria.