Abstract: Abstract 3936 The presence of CD19 in myelomatous plasma cells (MM-PC) correlates with adverse prognosis in MM. Although CD19 expression is up-regulated by CD81, this marker has been poorly investigated and its prognostic value in myeloma remains unknown. Herein, we assessed the frequency and the prognostic value of the immunophenotypic detection of CD81 surface expression in MM-PC of high-risk smoldering (SMM) and symptomatic MM patients at diagnosis and its role as a potential therapeutic target. The study included 230 elderly MM patients treated according to the Spanish GEM05 〉 65y trial, and a validation set based on 325 transplant candidates MM patients enrolled in the GEM05 〈 65y trial was used. In addition we analyzed a total of 56 high-risk SMM patients. The median follow-up was 32 and 22 months for the MM and SMM, respectively. Expression of CD81 on MM-PC was assessed by multiparameter flow cytometry (MFC). FISH was performed at baseline in immunomagnetic-enriched PCs from 211 of the 230 elderly MM patients, and in a subset of these patients (N=23) mRNA gene expression profiling (GEP) was also performed. MFC immunophenotyping showed the presence of CD81+ MM-PC in 20 of 56 (36%) SMM, and 90 of 230 (39%) MM patients. CD81+ SMM cases had a shorter TTP to symptomatic disease than CD81− patients (NR vs 37 months, P =.02). Similarly, CD81+symptomatic MM patients showed shorter PFS (3y: 29% vs 48%, P 〈 .001) and OS (3y: 64% vs 76%, P =.008) rates compared to CD81− cases. Multivariate analysis including other baseline variables showed that the best combination of independent predictive parameters for PFS were: CD81+ expression on MM-PC (HR=1.8; P =.004), high-risk cytogenetics (HR=1.8; P =.02) and percentage of MM-PC in S-phase ( 〉 2%; HR=1.7; P =.02); in turn for OS, CD81+ expression (HR=2.2; P =.005), high-risk cytogenetics (HR=2.2; P =.006) and age (≥75 years; HR=1.8; P =.03) were selected. To validate the adverse impact of CD81+ expression, we explored whether this new marker would retain its prognostic value in a series of 325 transplant candidates, symptomatic MM patients. CD81+ cases (138 out of 325, 42%) showed shorter PFS (3y: 44% vs 62%, P 〈 .001) and OS (3y: 74% vs 89%, P =.004) rates as compared to CD81− cases. The prognostic influence of CD81 expression prompted us to investigate its potential role as a therapeutic target in MM cell lines. 5 out of the 13 cell lines analyzed were homogeneously positive for CD81 (RPMI-8226, RPMI-LR5, NCI-H929, OPM-2, JJN3) while the others exhibited no expression; these results were further validated by western blotting. We then tested the effect of two different anti-CD81 antibodies on cell proliferation on 2 CD81+ cell lines (RPMI-8226 and JJN3) as well as in 1 CD81− (MM1S) MM cell line. Interestingly, the two antibodies tested decreased cell proliferation (around 30%, P ≤.005) in the two CD81+ cell lines, whereas no differences were found for the CD81− MM1S cell line. To assess whether anti-CD81 antibodies facilitate immune effector cell function, we performed in vitro ADCC. However, no effect was noted in the CD81+ RPMI-8226 cell line, using either PBMCs or the macrophage cell line RAW264.7, and at different cell ratios. Similar results were also found upon using CDC assay in CD81+ RPMI-8226 and JJN3 cell lines. Finally, we explored in a subgroup of MM patients (n=23) in which information was available, the relationship between positivity for CD81 by MFC and its genomic expression. The expression level of CD81 mRNA was significantly decreased in CD81− MM cases (P 〈 .001) vs. both healthy adults and CD81+ patients (P 〈 .001), with no significant differences between these two latter subgroups. Moreover, we found a highly significant correlation between the expression of CD81 mRNA by GEP and the percentage of CD81+ MM-PC by MFC (r=.812; P 〈 .001). We further investigated by GEP, differences in other genes involved in the CD81 signaling pathway, and CD81+MM patients showed significantly higher levels of CD79A (P =.03) and SYK (P =.02) mRNA than CD81−cases. In summary, our findings show the existence of a phenotypic-genomic correlation of CD81 expression in patients with myeloma. Expression of CD81 in MM-PC is an independent prognostic factor for patients with symptomatic MM and a marker for risk of progression in SMM. Blockage of CD81 with anti-CD81 antibodies does not show significant anti-myeloma activity; therefore, the precise mechanism of CD81 activation of MM-PC deserves further investigations. Disclosures: Paiva: Celgene: Honoraria; Janssen: Honoraria. Rosiñol:Janssen: Honoraria; Celgene: Honoraria. Mateos:Janssen: Honoraria; Celgene: Honoraria. Lahuerta:Janssen: Honoraria; Celgene: Honoraria. Blade:Janssen: Honoraria; Celgene: Honoraria. San Miguel:Janssen-Cilag: Honoraria; Celgene: Honoraria.

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: Abstract 1910 The outcome of multiple myeloma (MM) patients has markedly improved in the last decade. Thus, overall response rates between 85%-95%, with 30%-50% complete remission (CR) rates are now being reported in young patients treated with novel agents plus high-dose therapy/autologous stem cell transplantation (HDT/ASCT). A similar scenario is also emerging in the elderly (non-transplant candidates) population. Accordingly, more sensitive techniques are needed to assess patients’ response; these may contribute to compare the efficacy of different treatment schemas, to monitor minimal residual disease (MRD) and for prognostication. In the present study we have assessed the frequency and the prognostic value of IR by multiparameter flow cytometry in a total of 516 newly diagnosed MM patients included in three consecutive PETHEMA/GEM Spanish trials: two designed for transplant candidate patients - GEM 2000 (n=157) and GEM2005 〈 65y (n=206) - and one for elderly patients - GEM2005 〉 65y (n=153). The GEM2000 trial was based on 6 induction cycles of VBMCP/VBAD followed by HDT/ASCT; the GEM2005 〈 65y included three arms with 6 cycles each (Thalidomide/Dexamethasone -TD-, Bortezomib/Thalidomide/Dexamethasone -VTD- and, VBMCP/VBAD with Bortezomib in the two final cycles -VBMCP/VBAD/Bortezomib) followed by HDT/ASCT; and the GEM2005 〉 65y compared 6 cycles of Bortezomib/Melphalan/Prednisone -VMP- vs. Bortezomib/Thalidomide/Prednisone -VTP-. All three trials had in common that patients received 6 induction cycles and IR was evaluated at this time point. In addition, IR was assessed on day +100 after HDT/ASCT in the first two trials. Patients were defined to be in IR when myelomatous plasma cells (MM-PCs) were undetectable by MFC or when less than one phenotypically aberrant PC was detected among 104 cells analyzed. Patients were referred for MRD studies if they were mainly in CR or VGPR. The IR rates reported here were calculated on intention to treat analysis. Figure 1 summarizes the IR rates after induction. The lowest IR rates corresponded to the VBMCP/VBAD and TD schemes (5% and 6%, respectively) while with the bortezomib-based regimens an approximately 3-fold increment in the IR rates was observed: VTP (12%), VBMCP/VBAD/Bortezomib (15%), VMP (16%) and VTD (17%). After HDT/ASCT, IR rates were found to be significantly increased (p 〈 .001) in the GEM2000 protocol (14%) and in all arms of the GEM2005 〈 65y trial: TD (18%), VBMCP/VBAD/Bortezomib (30%) and VTD (34%). Thus, a minimum 2-fold increment of IR rates was further achieved after HDT/ASCT. In addition, IR rates achieved after HDT/ASCT in patients included in all three arms of the GEM2005 〈 65y trial were significantly superior (p≤.008) to cases treated according to the GEM2000 protocol, indicating that induction regimens with novel agents improved post-transplantation rates of IR. Moreover, bortezomib-based regimens vs. TD were associated with increased IR rates not only before but also after HDT/ACSCT (p=.06 and p=.02 for VBMCP/VBAD/Bortezomib and VTD, respectively). We further compared the impact of achieving an IR after induction and at day+100 after HDT/ASCT in the progression-free (PFS) and overall survival (OS) within the three protocols. Patients in IR status after an induction regimen according to the GEM2000, GEM2005 〈 65y and GEM2005 〉 65y protocols showed significantly longer (p 〈 .001) 3-year PFS rates (100%, 100% and 90%, respectively) compared to patients in a no-IR status (61%, 59% and 35%, respectively). Similarly, 3-year OS rates were significantly longer (p=.01) in IR vs. no-IR patients status (100%, 100% and 94% vs. 84%, 90% and 76% for the GEM2000, GEM2005 〈 65y and GEM05 〉 65y protocols, respectively). Likewise, an IR vs. no-IR status after HDT/ASCT in both the GEM2000 and GEM05 〈 65y trials was also associated with significantly increased 3-year PFS (p 〈 .001) and OS (p=.007) rates. In summary, this study demonstrates that the achievement of an IR is a strong prognostic factor regardless of the type of treatment; thus, higher IR rates may help to identify optimal therapeutical schemes. In this sense, HDT/ASCT is able to markedly increase IR rates after induction even in the era of novel agents, and this translates into extended survival. Disclosures: Off Label Use: VTP is not approved for the treatment of newly diagnosed myeloma patients and VT and VP are not approved for maintenance therapy. None of the combinations proposed, VBCMP/VBAD plus bortezomib, VT and VTD are approved as induction therapy in newly diagnosed myeloma patients. Mateos:Janssen Cilag: Honoraria; Celgene: Honoraria. Rosiñol:Janssen-Cilag: Honoraria; Celgene: Honoraria. Cibeira:Janssen-Cilag: 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. Oriol:Janssen-Cilag: Honoraria; Celgene: Honoraria. de Arriba:Janssen-Cilag: Honoraria; Celgene: Honoraria. Palomera:Janssen Cilag: Honoraria. De La Rubia:Janssen-Cilag: Honoraria; Celgene: Honoraria. Díaz-Mediavilla:Janssen-Cilag: Honoraria; Celgene: Honoraria. Garcia-Laraña:Janssen Cilag: Honoraria; Celgene: Honoraria. Sureda:Janssen-Cilag: Honoraria; Celgene: Honoraria. Alegre:Janssen-Cilag: Honoraria; Celgene: Honoraria. Blade:Janssen cilag: Honoraria; Celgene: Honoraria. Lahuerta:Janssen-Cilag: Honoraria; Celgene: Honoraria. San Miguel:Janssen-Cilag: 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; Millennium: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Abstract: Abstract 3938 The incorporation of high-dose therapy/autologous stem cell transplantation (HDT/ASCT) and novel agents has significantly improved survival of MM young pts; however, the molecular heterogeneity of the disease warrants the investigation if such improvement also benefits patients harboring poor prognostic features such as non hyperdiploid (HY) karyotypes and high proliferation index. Herein, we have analyzed by MFC the DNA ploidy status and proliferation of bone marrow (BM) PC in a total of 595 newly diagnosed MM pts included in two consecutive PETHEMA/GEM trials: GEM2000 (VBMCP/VBAD followed by HDT/ASCT; N=319) 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=276). Baseline FISH analysis were performed on separated PC. DNA ploidy and cell cycle were assessed by MFC through simultaneous staining with CD38/CD138 and propidium iodide. Median follow-up of the whole series was 38 months. Of the 595 pts, 295 were classified as non-HY (49.6%) and 300 as HY (50.4%). Patients with non-HY vs HY DNA content showed significantly inferior median PFS (34 vs 44 months, P=.004) and OS (67 vs 84, P=.005). Interestingly, we have detected by MFC the presence of two different PC clones (with different DNA ploidy status) in 34 of the 595 (6%) patients, and this subgroup showed a poor outcome (median PFS and OS of 26 and 52 months respectively, P≤.005). Regarding the proliferative index, the median percentage of PCs in S-phase in the whole series was of 1.14% (0%-13%). Accordingly, pts were stratified using a cutoff of ≥1% vs 〈 1% PCs in S-phase, which translated in significantly different PFS (medians of 34 vs 43 months, P 〈 .001) and OS (medians of 66 vs 93 months, P=.001). Of note, the detection of a proliferative rate ≥3% also identified a subgroup of patients (92 of 595, 15%) with high-risk disease (median PFS and OS of 22 and 45 months respectively, P≤.001). At the multivariate analysis including other baseline prognostic factors, the presence of high-risk cytogenetics (HR=1.7;P=.007), ≥1% PCs in S-phase (HR=2.0;P 〈 .001), 〉 15% PCs by MFC (HR=1.7;P=.008) and 〉 5% normal PCs within the BM PC compartment (HR=6.6;P=.008) emerged as independent prognostic factors for PFS; in turn, for OS the presence of high-risk cytogenetics (HR=2.3;P 〈 .001), non-HY DNA content (HR=1.7;P=.02), ≥1% PCs in S-phase (HR=2.0;P=.002) and the ISS disease stage (HR=1.7;P=.03) were selected. After this analysis of the overall population, we investigated whether the incorporation of novel agents in the induction regimen previous to HDT/ASCT could abrogate the poor prognosis of patients classified as non-HY and with ≥1% PCs in S-phase. Patients with non-HY DNA status included in the GEM2005 〈 65y trial do not show significantly superior PFS (40 vs 34 months, P=.8) nor OS (not reached vs 63 months, P=.5) compared to cases enrolled in the GEM2000 protocol. Focusing on pts with ≥1% PCs in S-phase, no differences were founded for PFS (40 vs 33 months, P=.9), but OS was significantly longer for patients treated with novel agents prior to HDT/ASCT (NR vs 61months, P=.004). Finally, we wanted to gain further insight into the potential association between specific cytogenetic abnormalities and PC proliferation, as well as whether there is a difference in the proliferative rate of PCs between diagnosis and disease progression. Interestingly, pts harboring a t(11;14) showed a significantly decreased percentage of PCs in S-phase (0.7% vs 1.2%, P 〈 .001), while no differences were recorded for t(4;14), t(14;16), del(Rb) and del(17p). To address our final question, we compared the proliferative rate of PCs from 52 pts with paired BM samples at diagnosis and at relapse. Of note, 45 of the 52 (85%) pts showed an increased percentage of PCs in S-phase at relapse, with a median 2-fold difference between the proliferative rate at diagnosis vs. relapse (P 〈 .001). In summary, our results show that the evaluation of PCs DNA content by MFC immunophenotyping provides valuable clinical information, as pts with a non-HY DNA status and high proliferative rate show a poor outcome, which is not yet fully abrogated by the incorporation of novel agents prior to HDT/ASCT. Moreover, pts at relapse show an increased proliferative index; therefore, the precise mechanisms leading to PC proliferation deserves further investigations. Disclosures: Paiva: Celgene: Honoraria; Janssen: Honoraria. Rosiñol:Janssen: Honoraria; Celgene: Honoraria. Mateos:Janssen: Honoraria; Celgene: Honoraria. Alegre:Janssen: Honoraria; Celgene: Honoraria. Lahuerta:Janssen: Honoraria; Celgene: Honoraria. Blade:Janssen: Honoraria; Celgene: Honoraria. San Miguel:Janssen-Cilag: Consultancy; Celgene: Consultancy; Millennium Pharmaceuticals, Inc: Consultancy.

Abstract: The achievement of complete response (CR) after high-dose therapy/autologous stem cell transplantation (HDT/ASCT) is a surrogate for prolonged survival in multiple myeloma; however, patients who lose their CR status within 1 year of HDT/ASCT (unsustained CR) have poor prognosis. Thus, the identification of these patients is highly relevant. Here, we investigate which prognostic markers can predict unsustained CR in a series of 241 patients in CR at day +100 after HDT/ASCT who were enrolled in the Spanish GEM2000 (n = 140) and GEM2005 〈 65y (n = 101) trials. Twenty-nine (12%) of the 241 patients showed unsustained CR and a dismal outcome (median overall survival 39 months). The presence of baseline high-risk cytogenetics by FISH (hazard ratio 17.3; P = .002) and persistent minimal residual disease by multiparameter flow cytometry at day +100 after HDT/ASCT (hazard ratio 8.0; P = .005) were the only independent factors that predicted unsustained CR. Thus, these 2 parameters may help to identify patients in CR at risk of early progression after HDT/ASCT in whom novel treatments should be investigated.

Abstract: Abstract 630 The achievement of CR after high-dose therapy/ASCT (HDT/ASCT) is a surrogate for prolonged survival in MM. While this is well accepted, the long-term clinical outcome of MM patients achieving CR is still heterogeneous and a small fraction of patients unexpectedly lose their CR status early on after HDT/ASCT and experience a dismal survival. In fact, survival of patients with unsustained CR is even poorer than that of those not achieving CR. Herein we sought to identify prognostic markers predictive of unsustained CR after HDT/ASCT. The study included a total of 241 patients achieving CR at day+100 after HDT/ASCT treated in two consecutive GEM/PETHEMA trials: GEM2000 (VBMCP/VBAD, n=140) 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=101). All cases were referred for MRD assessment by MFC at day+100 after HDT/ASCT; baseline FISH analysis were available in 110 of the 241 patients. We first investigated which of the most relevant disease characteristics had prognostic influence in patients in CR at day+100 after HDT/ASCT. In this cohort some markers with consistent influence in unselected MM populations such as patient age, ISS stage, serum β2-microglobulin, BMPC burden and % of PC in S-phase were not significantly predictive. In contrast, the presence of baseline anemia was a significant prognostic marker for OS (P=.01). Regarding cytogenetics, 16% of CR patients were considered with high-risk disease at presentation and showed a significantly inferior TTP (3-years, 40% vs 79%; P=.001) and borderline OS (3-years, 73% vs 96%; P=.07) compared to cases with standard-risk. In addition, MFC immunophenotyping showed persistent MRD in 87 of the 241 (36%) CR patients, and the failure to achieve an immunophenotypic CR at day+100 after HDT/ASCT resulted in significantly inferior TTP (3-years, 58% vs 85%; P 〈 .001) and OS (3-years, 80% vs 90%; P=.001). In the multivariate analysis, the best combination of independent predictive parameters for TTP were immunophenotypic CR status (P 〈 .001;HR=7.1) and FISH cytogenetics (P 〈 .001;HR=5.6); in turn, for OS immunophenotypic CR status (P=.001;HR=7.7), FISH cytogenetics (P=.01;HR=5.1) and age ≥60 years (P=.03;HR=3.4) were selected. We further explored the clinical impact of the immunophenotypic CR in the context of standard-risk and high-risk disease. The best prognosis was for patients with both standard-risk cytogenetics and in immunophenotypic CR (3y: TTP, 92%; OS, 100%), while the worst outcome occurred in cases with both high-risk disease and persistent MRD (3y: TTP, 0%; OS, 32%). The two other categories had an intermediate prognosis, although it was better for patients with high-risk cytogenetics achieving an immunophenotypic CR (3y: TTP, 69%; OS, 100%) than for patients with standard-risk disease but failing to achieve an immunophenotypic CR after HDT/ASCT (3y: TTP, 57%; OS, 90%). We then investigated the parameters that could help to identify patients in CR at risk of early relapse after HDT/ASCT. Of the 241 patients, 30 (12%) progressed within 1 year after HDT/ASCT (unsustained CR) and this subgroup showed a dismal outcome, with a median OS of only 39 months (P 〈 .001). Patients with unsustained CR showed significantly higher incidence of anemia at baseline (48% vs 24%, P=.01), advanced ISS stage 2 or 3 (86% vs 55%, P=.003), high-risk cytogenetics (40% vs 10%, P=.005) and persistent MRD by MFC (63% vs 32%, P=.001) compared with the remaining cases. At the multivariate analysis, only cytogenetic abnormalities (P=.002;HR=12.5) and the immunophenotypic CR status at day+100 after HDT/ASCT (P=.001;HR=8.8) emerged as independent predictive markers for unsustained CR. Based on these two variables, we established a predictive index by assigning one point for each adverse factor. Accordingly, 3 risk groups of patients in CR after HDT/ASCT were defined, with significantly (P 〈 .001) different rates of disease progression within the first year after HDT/ASCT for patients with none, one, or both risk factors (7%, 20% and 100%, respectively; Figure). Our results show that the baseline evaluation of cytogenetic abnormalities combined with response assessment by MRD after HDT/ASCT can discriminate a subset of CR patients with a dismal outcome who should be candidates for novel treatment strategies after HDT/ASCT. Disclosures: Paiva: Celgene: Honoraria; Janssen: Honoraria. Rosiñol:Janssen: Honoraria; Celgene: Honoraria. Mateos:Janssen: Honoraria; Celgene: Honoraria. Cibeira:Janssen: Honoraria; Celgene: Honoraria. Alegre:Janssen: Honoraria; Celgene: Honoraria. Lahuerta:Janssen: Honoraria; Celgene: Honoraria. Blade:Janssen: Honoraria; Celgene: Honoraria. San Miguel:Janssen-Cilag: Honoraria; Celgene: Honoraria.

Abstract: Abstract 3 In elderly pts with newly diagnosed MM, the VISTA trial has demonstrated that the combination of bortezomib plus melphalan – prednisone (VMP) is significantly superior to MP alone. However, it remains to be elucidated which agent is the optimal partner for bortezomib: an alkylating agent or an immunomodulatory drug. In order to answer this question, Spanish Myeloma Group activated a phase III trial comparing VMP versus VTP (T for thalidomide) as induction therapy. To evaluate if the treatment regimen could be further optimized by decreasing the toxicity while maintaining efficacy, the intensity of both schedules of induction was reduced as compared with the VISTA regimen but supplemented with maintenance therapy. Between April 2005 and October 2008, 260 pts were randomized to receive 6 cycles of VMP vs VTP as induction therapy followed by maintenance with VT vs VP for up to three yrs. In the VMP arm pts received bortezomib 1.3 mg/m2 twice weekly (days 1, 4, 8, 11; 22, 25, 29 and 32) for one 6-week cycle, followed by once weekly (days 1, 8, 15 and 22) for five 5-week cycles in combination with oral melphalan 9 mg/m2 and prednisone 60 mg/m2 once daily on days 1–4 of each cycle. In the VTP arm pts received the same bortezomib and prednisone, but instead of melphalan they received thalidomide at a dose of 100 mg daily. Following the 6 cycles of induction, pts moved into maintenance that consisted in a conventional cycle of bortezomib, 1.3 mg/m2 twice weekly (days 1, 4, 8, 11) administered every three months in combination with either continuous thalidomide, 50 mg daily (VT) or prednisone, 50 mg on alternate days (VP). 253 pts are evaluable for response to induction; 125 were assigned to receive VMP and 128 to VTP. Regarding baseline characteristics, both arms were well balanced. Response rate to induction therapy was similar in both arms: ≥ PR in 81 and 79% of pts treated with VMP and VTP respectively, with a CR rate of 22% vs 27% (p=NS) and CR+nCR of 36% in both arms. Only two pts progressed under induction treatment in each arm. After a median follow-up of 22m (8-40), there weren't significant differences in terms of 2-y TTP (VMP 75% vs VTP 70%), PFS (VMP 71% vs VTP 61%) and OS (VMP 81% vs VTP 84%). 178 pts were randomized to maintenance and 143 are evaluable for efficacy. Overall, maintenance therapy was able to increase the CR rate from 25% (mean obtained after induction therapy) up to 42%, with no significant differences between VT and VP arms (46 and 38%). After a median duration of maintenance of 13 m there is a trend in favour of VT in terms of 1-y TTP (84% vs 71%; p=0.05), without differences in 1-y OS (92% for VT vs 89% for VP). 27 pts presented high-risk cytogenetic abnormalities (CA) ((4;14)t, (14;16)t, del[17p]); the CR rate was similar in this high-risk group as compared with standard risk group (26% vs 25% after induction and 42% after maintenance in both groups). There aren't differences between high-risk and standard-risk pts in the 2-y TTP (74% vs 73%) and 2-y OS (77% vs 81%) from inclusion; however, there is a trend to lower 1 y-TTP from the time to randomization to maintenance for the high-risk group compared to the standard-risk (68% vs 79%) without differences in 1 y-OS (90% vs 93%). Regarding toxicity, during the induction therapy, VMP resulted in higher incidence of ≥G3 neutropenia than VTP (37 vs 21%) and this translated into more ≥G3 infections (7 vs 〈 1%); 8,5% of pts receiving VTP developed ≥G3 cardiac events (cardiac failure (5), atrial fibrillation (2), hypotension (2), heart attack (1) and AV blockage (1)). The incidence of ≥G3 PN was 5% in VMP and 9% in VTP (p=NS). During maintenance therapy, the most relevant ≥G3 toxicities included: cardiac events in 2 pts in VT (supraventricular arritmia (1) and heart attack (1)) vs 1 in VP (cardiac failure); G-I events in 4 pts in VT vs 1 in VP; finally, only one patient in VT arm died during the maintenance therapy due to sepsis. In summary the current results indicate that: 1. both modified induction schedules (VMP and VTP) are highly effective with similar ORR and CR rates, but a clear different toxicity profile (more neutropenia, but less cardiac toxiciety and PN with VMP); 2. maintenance therapy with either VT and VP markedly improve the quality of responses with a good safety profile; and finally 3. the combination of these induction and maintenance schedules seems to overcome the poor prognosis of high-risk CA in elderly MM patients. Disclosures: Mateos: Janssen Cilag: Honoraria, Speakers Bureau; Celgene corporation: Honoraria, Speakers Bureau. Off Label Use: VTP is not approved for the treatment of untreated MM patients. Cibeira:Jansen-Cilag: Honoraria; Celgene: Honoraria. Gutiérrez: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. San-Miguel:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Millennium: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen–Cilag: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Abstract: Standard first-line treatment for elderly multiple myeloma (MM) patients ineligible for stem cell transplantation is melphalan plus prednisone (MP). However, complete responses (CRs) are rare. Bortezomib is active in patients with relapsed MM, including elderly patients. This phase 1/2 trial in 60 untreated MM patients aged at least 65 years (half older than 75 years) was designed to determine dosing, safety, and efficacy of bortezomib plus MP (VMP). VMP response rate was 89%, including 32% immunofixation-negative CRs, of whom half of the IF– CR patients analyzed achieved immunophenotypic remission (no detectable plasma cells at 10–4 to 10–5 sensitivity). VMP appeared to overcome the poor prognosis conferred by retinoblastoma gene deletion and IgH translocations. Results compare favorably with our historical control data for MP—notably, response rate (89% versus 42%), event-free survival at 16 months (83% versus 51%), and survival at 16 months (90% versus 62%). Side effects were predictable and manageable; principal toxicities were hematologic, gastrointestinal, and peripheral neuropathy and were more evident during early cycles and in patients aged 75 years or more. In conclusion, in elderly patients ineligible for transplantation, the combination of bortezomib plus MP appears significantly superior to MP, producing very high CR rates, including immunophenotypic CRs, even in patients with poor prognostic features.

Abstract: Abstract 617 Disappearance of normal bone marrow (BM) plasma cells (N-PC) predicts malignant transformation of monoclonal gammopathy of undetermined significance (MGUS) and smoldering myeloma (SMM) into symptomatic myeloma (MM). The homing, behavior and survival of N-PC, but also CD34+ hematopoietic stem/precursor cells (HPC), B-cell precursors, and (mono)clonal/aberrant PC (M-PC) largely depends on their interaction with SDF-1 expressing BM stromal cell niches. Accordingly, it can be hypothesized that a certain degree of competition among BM B-cell precursors, CD34+ HPC, and PC exist for the same BM niches. Thus, progressive replacement of normal cells by M-PC could help to explain the occurrence of cytopenias and hypogammaglobulinemia in MM patients. However, this hypothesis has not been investigated in depth neither in MM nor in SMM and MGUS. In this study we analyze by 8-color multiparameter flow cytometry the distribution and competitive migration capacity of B-cell precursors, CD34+ HPC, N-PC and M-PC in the BM and PB of patients with MGUS (n=60), SMM (n=47) and MM (n=87) at diagnosis plus 12 MM cases studied after high-dose therapy/autologous stem cell transplantation (MM POST-HDT/ASCT) vs. healthy adults aged 〉 60 years (HA; n=26). The percentage of BM M-PC as well as the number of M-PC from all BMPC found at diagnosis significantly (p 〈 .001) increased from MGUS to SMM and MM patients. Circulating M-PC were also detected at diagnosis in the PB of MGUS (21%) vs. SMM (69%) and MM (75%) at increasing M-PC counts (p≤.002). Interestingly, PB vs. BM M-PC showed significantly lower amounts of sideward light scatter (p 〈 .001), together with lower levels of CD38 (p=.001), CD40 (p=.006), CD56 (p=.03) and CD138 (p=.02) expression. Focusing on the CXCR4-SDF1 axis, we found that the proportion of CXCR4+ PC slightly decreased (p 〉 .05) from N-PC from HA (42%) to M-PC from MGUS (39%), SMM (37%) and MM (35%) patients at diagnosis, while MM POST-HDT/ASCT cases showed the lowest values (28%). In contrast, plasma levels of SDF-1 increased from HA (1150 pg/mL) to MGUS (1352 pg/mL), SMM (1656 pg/mL) and MM (1778 pg/mL; p=.04 vs. HA) patients, returning to almost normal levels in MM POST-HDT/ASCT (1331 pg/mL). Thus, an inverse correlation trend (r2=.12; p=.05) between the proportion of CXCR4+ PC and SDF-1 plasma levels was found. Concerning the distribution of the normal cell populations, BM pro-B and pre-B cell precursors were significantly decreased in MM (p=.001) patients vs. HA, while it was normal in MGUS (p 〉 .05) and SMM (p 〉 .05). Despite the number of N-PC in the BM was significantly lower among MM and SMM vs. MGUS cases (p 〈 .001), the distribution of circulating N-PC in PB was normal in all three groups of patients (p 〉 .05 vs. HA). Interestingly however, the proportion of CXCR4+ PB N-PC progressively increased from HA (11%) to MGUS (14%), SMM (15%) and MM (21%; p=.05 vs. HA), while MM POST-HDT/ASCT cases showed the lowest median percentage of CXCR4+ PB N-PC (5%). CD34+ HPC were found to be depleted in the BM of MM (0.3%; p=.001) and SMM (0.4%; p=.002) patients vs. HA (0.9%) while MGUS (0.8%) and MM POST-HDT/ASCT (1.1%) patients showed normal CD34+ HPC numbers. Conversely, PB CD34+ HPC progressively increase from HA to MGUS, SMM and MM cases (p=.008 and p=.06 vs. HA, respectively). By contrast, in MM POST-HDT/ASCT patients the number of PB CD34+ HPC returned to normal/lower levels. Ex-vivo competition assays between BM B-cells, PC and CD34+ HPC for SDF-1 induced migration showed that in HA, CD34+ HPC displayed the highest migration potential in the presence of SDF-1, followed by pre-B cell precursors; conversely N-PC barely migrated. No significant differences were found for the migration of all cell populations analyzed between MGUS and SMM patients vs. HA, except for M-PC that showed an impaired migration in the presence of SDF-1. In turn, the migration potential of CD34+ HPC (p=.04), and pre-B cell precursors (p=.02) was markedly reduced in symptomatic MM, particularly at lower SDF-1 concentrations (30nM). Most interestingly, the migration of M-PC from symptomatic MM was markedly increased at both concentrations of SDF-1 used: median of 2.9% and 1.0% for SDF-1 concentrations of 30nM and 70nM, respectively. Overall, these findings provide evidence about the role of progressive competition and replacement of normal BM cells by M-PC in determining transformation of pre-malignant MGUS and SMM into symptomatic MM. Disclosures: No relevant conflicts of interest to declare.