ALBERT

Description: INTRODUCTION In newly diagnosed Multiple Myeloma (MM) patients (pts), Copy Number (CN) losses of chromosome 17p13, carrying the TP53 tumor-suppressor gene, are strong predictors of poor outcomes. On the contrary, the prognostic relevance of TP53 mutations at the onset of the disease is less clear, due to the very limited frequency of clonal lesions, as revealed by Sanger sequencing. To address this poorly investigated issue, we used an ultra-deep sequencing (UDS) approach to characterize the TP53 structural architecture in both newly diagnosed and relapsed MM pts and to assess the prognostic role and evolution over time of small TP53 mutated sub-clones. SAMPLES AND METHODS A cohort of 99 newly diagnosed MM pts treated up-front with bortezomib-based regimens and autologous stem cell transplantation, was included in this molecular study. In 29 cases, samples were collected both at diagnosis and at relapse(s). DNA was obtained from CD138+ highly purified plasma cells. TP53 gene mutational status was analysed by using an amplicon-targeted UDS approach (GSJ, 454 Roche Life Sciences). In order to discriminate between low frequency sub-clonal TP53 variants and sequencing errors, sequencing raw data were filtered according to cut-off values based on different ranges of sequences' coverage depth. Additional filters were also applied, based on both quality and biological cut-offs, to obtain a final confident list of variants. Analysis of CN alterations (CNAs) was performed by SNPs array and results analysed with ChAS software. RESULTS With a median coverage of 1386X, a list of 129 correctly called TP53 variants (either missense, or nonsense or splice ones), including 20 INDELs, was detected. Only deleterious and N/A variants (according to SIFT classification) were included in the list. Most newly diagnosed MM pts (55%) carried at least one TP53 sub-clonal variant (on average 1.08 variants per pts), with 45/99 (45%) carrying non-mutated TP53. Pts carrying TP53 sub-clonal variants bared also TP53 CN hemizygous losses (20%), CKS1B gains (56%) and cdkn2c losses (14%). According to TP53 sub-clonal mutational load, pts were stratified in two sub-groups, including 28 pts with ≥2 (high load) and 71 with

Description: Abstract 1810 Background. The efforts to characterize the genomic background of Multiple Myeloma (MM) and to correctly stratify at diagnosis patients (pts) subsequently treated with novel drugs thoroughly meet the clinical requirement to handle highly powerful prognostic factors. On the other hand, the information obtained from each pts needs to be carefully interpreted, by considering the genomic background as a whole, since each aberration might represent the different expression of a common deregulated pathway. The TP53 deletion on chromosome (chr) 17p13 represents one of the genomic aberration most significantly associated with poor outcome in MM. Overall, the TP53 tumor-suppressor gene inactivation has a central role in the tumorigenesis, since p53 is the most frequently mutated protein in human cancers. The p53 pathway silencing might pass also through changes in the expression level or activation of p53 itself, regulated by several specific inhibitors and/or activators. One of the most potent inhibitor of p53 is MDM4, which is critical for control of p53 activity during response to stress and is often amplified in several types of tumors. The MDM4 locus is located on chr1q32.1, a region frequently amplified in MM. Aim. Since in MM the TP53 deletion on chr 17p13 is reported with low frequencies (7 to 11% at diagnosis) and since the vast majority of hemizygous TP53 deleted pts do not harbor mutations on the allele not affected by the deletion, we sought to investigate the frequency and the prognostic role of TP53 deletion and/or MDM4 amplification in newly diagnosed MM pts, assuming that both of these chromosomal aberrations might contribute to impaired p53 function. All pts have been treated with bortezomib-thalidomide-dexamethasone (VTD) as induction therapy prior to, and as consolidation after, double autologous stem-cell transplantation (ASCT). Pts and methods. Eighty-nine pts treated with VTD incorporated into double ASCT were analyzed at diagnosis by means of unpaired analysis of copy number alterations (CNA) (Affymetrix 6.0 SNP array), gene expression profile (GEP) (Affymetrix U133 Plus2.0 array) and Real-time PCR; the genomic results have been analyzed in the clinical context. Results. The CNA analysis showed that 9/89 pts (10%) carried a minimal deleted region of 482 Kb on chr17p13.1, including TP53, and that 27/89 pts (30,3%) carried a minimal amplified region of 1.1 Mb on chr1q32.1 including MDM4. Pts were stratified into two subgroups according to the presence of amplified MDM4 and/or deleted TP53 (group A, 34 pts, or 38%) or the absence of both these abnormalities (group B, 55 pts, or 62%). Baseline clinical characteristics were homogeneous, except for a higher rate of IgA isotype in group A. On the contrary, groups A and B were clearly imbalanced with respect to the genomic background: indeed, the t(4,14) frequency, as well as the average number of CNAs were overall higher in group A as compared to group B (38% vs. 14% t(4;14) positive, p=0.0002 and 165 vs 103 CNAs, p = 0.03). A GEP comparison among the two groups of pts highlighted an overall deregulation of pathways related to the cell cycle, the DNA damage repair and the cell adhesion and cytoskeleton remodeling, due to the differentiated expression of 627 probes-set in group A vs group B pts (false discovery rate

Description: Background. Array-based technology has been showing a great impact on clinical cancer cytogenetic, especially on genetically heterogeneous disease, such as MM, where relevant lesions might be the hallmarks of different patients’ subgroups, thus becoming of clinical relevance as well. We present herein the results of a molecular sub-study of the EMN02 phase III study (EMN02_HOVON95) which was designed to compare consolidation therapy Bortezomib, Melphalan and Prednisone versus upfront autologous stem cell transplantation, both applied after induction therapy with bortezomib-cyclophosphamide-dexamethasone (VCD). The sub-study was aimed at developing a comprehensive, high throughput genomic profile to be used to stratify uniformly treated MM patients according to their genomic background at baseline and to perform correlations with response to induction therapy. Patients and methods. Data obtained from 170 patients who consecutively entered the study and received three 21-day cycles of VCD induction therapy were analyzed. Baseline patients’ characteristics, including cytogenetic abnormalities, were comparable with those of 717 patients enrolled by participating Italian centres. Highly purified CD138+ bone marrow plasma cells were profiled by SNPs array (Affymetrix 6.0 and CytoScanHD® chip). ChAS (Affymetrix) and Nexus Copy NumberTM 7.5 (Biodiscovery) software were used to perform Copy Number Alterations (CNAs) analyses and clinical correlations, respectively. Results. After induction therapy, 66 out of 170 (38.8%) patients achieved a very good partial response (VGPR) or better, including 15 (8,8%) who attained a complete response (CR). On the contrary, 104/170 (61.1%) patients achieved

Description: Background Although remarkable advances have been achieved in MM therapy, mainly thanks to the introduction of novel-agent-based regimens, the disease remains incurable. Neoplastic CD138+ plasma cells are the hallmark of MM: both their expansion in the bone marrow (BM) and the production of monoclonal immunoglobulin (Ig) are responsible for the clinical manifestation of the disease. However, the existence of a Myeloma Propagating Cells (MPCs) has been proposed as a major cause of MM drug-resistance, leading to relapse. Several studies support the hypothesis that MPCs are phenotypically close to memory B cells residing in the CD138- compartment; however, very little is known concerning their molecular characteristics. Here we present an extensive molecular characterization of clonotypic CD19+ B cells clones obtained from newly diagnosed MM patients (pts), in order to recognize biological pathways possibly explaining the malignant clone’s persistence. Methods CD138+ and CD138- cell fractions were collected from BM and peripheral blood (PBL) of 50 newly diagnosed MM pts. CD19+ B cell and CD27+ memory B cell populations were isolated from CD138- cell fraction. Clonogenic assays were performed by plating cell fractions obtained from RPMI-8226 and NCI-H929 cell lines. The molecular characterization included: IgH gene rearrangement Sanger sequencing; analysis of the whole spectrum of genomic aberrations and gene expression profiling, by Affymetrix 6.0 SNPs array and HG-U133 Plus 2.0 microarray, respectively. Results Clonogenic assays showed that CD138- cells, plated on conditioned media, were able to form colonies after two weeks of culture more efficiently than CD138+ cells. By VDJ gene rearrangement sequencing, a clonal relationship between the CD138+ clone and the memory B ones was confirmed. SNPs arrays showed that both BM and PBL CD138+ cell fractions carried exactly the same genomic macro-alterations. On the contrary, in the CD138-19+27+ cell fractions from BM and PBL any macro-alteration was detected, whereas several micro-alterations (median number per sample: 32 amplifications and 16 losses, range: 8-122 Kb, average markers per region: 50) unique of the memory B cells clone were highlighted. An enrichment analysis revealed the involvement of genes affected by losses (17 genes) in both DNA repair mechanisms and transcriptional regulation and the involvement of genes affected by gains (46 genes) in both the negative regulation of apoptosis and the angiogenesis. Interestingly, KRAS, WWOX and XIAP genes, renown to be involved in MM pathogenesis, are located in the amplified regions in the immature cells. Moreover, several LOH regions were described, which covered at least 106 tumor suppressor genes involved in MM and leukemia (including TP53, CDKN2C and RASSF1A). Transcriptome profiles analysis of the CD19+ cell fractions highlighted pathways suggesting a possible involvement of immature cells in MM pathogenesis. The gene expression profiles of 20 MM CD19+ cells samples (12 from PBL, 8 from BM) were compared both to their normal counterpart and to the mature CD138+ cell fractions. In particular, unsupervised analysis by hierarchical clustering discriminated the differential expression of 11480 and 11360 probes in the PBL and BM CD19+ clones, respectively (2; FDR=0,05; p

Description: Abstract 2901 Hypoxia-inducible factor-1 alpha (HIF1 α) is a transcription factor that plays a critical role in survival and angiogenesis. In solid tumors, elevated expression of HIF-1 α, in response to hypoxia or activation of growth factor pathways, is associated with tumor proliferation, metastasis, and drug resistance and correlated with poor prognosis. In contrast to solid tumors, the role of HIF1 α in hematological malignancies is not completely known. In particular in multiple myeloma (MM) HIF1 α has been suggested to be constitutively expressed and HIF1 α knockdown cell lines have shown higher sensitivity to standard chemotherapy, suggesting a role in the pathophysiology of MM. In the present study, we explored the effect of EZN2968, an antisense oligonucleotide against HIF1 α, as a molecular target in MM. We showed, using real time PCR, and Western blotting analysis, that the expression of HIF1 α in several MM cell lines (MM1S, U266, OPM2, RPMI8226) is detectable under conditions of normoxia or hypoxia and is increased in the presence of growth stimuli (IL-6 and stroma cells). The immunofluorescence analysis suggested that the protein is ubiquitously present in both the cytosol and nucleus. To evaluate the specificity of the oligonucleotide for the target, we tested whether EZN2968 was able to induce a selective and stable down-modulation of HIF1 α mRNA and protein expression. We confirmed that the downmodulation was lasting in a long term culture experiment (up to 96 hours) either in normoxic or hypoxic conditions, and did not affect the expression of other family members of hypoxia inducible transcription factors (HIF2 α). We next explored the effects of EZN-2968 on the growth and survival of MM cells. Using an MTT colorimetric survival assay, we showed that, after 48 hours of culture in the presence of the HIF1 α inhibitor (20μM), MM1.S and U266 cell lines exhibited a reduction of 30% of viability compared to untreated cells, while RPMI8226 of 15%. AnnexinV/PI staining revealed that EZN-2968 (20μM) increased, after 48 hours of culture, the percentage of PI+ cells compared to the control, suggesting a disruption on membrane permeability. In addition, immunoblotting revealed PARP cleavage as early as 24 hours. Evaluation of cell cycle profile, by flow cytometric analysis, showed an increase of the sub-G0/G1 population from 3.5% to 30 %, after 48 hour of exposure to EZN-2968. To evaluate if the impact on cell viability was irreversible, we performed a cell death commitment assays. MM1S cells were incubated with EZN2968 (20 μM) for 24 to 96 hours, following incubation in drug-free medium for additional 24 to 72 hours. MTT colorimetric survival assay showed that EZN-2968 treatment for as early as 24h resulted in commitment to death in all cell lines tested. To evaluate the effect of microenvironment, MM cells treated with EZN2968 were exposed to IL-6 and stroma cells for additional 24 hours. EZN2968 overcame the proliferative effect induced by cytokines. We next evaluated the impact of EZN-2968 on purified CD138+ cells from MM patients with advanced MM. MTT colorimetric survival assay showed a reduction of cells viability of 30% after 24 hours of incubation. In addition we observed a low sensitivity of PBMCs and CD34+cells, derived from healthy donors, to EZN-2968 treatment suggesting that EZN-2968 has selective in vitro activity against MM cells. Evaluation of gene expression profiling modulation induced by EZN 2968 is on going. In summary, our results suggests that the inhibition of HIF1 α activity can be used as an attractive therapeutic target for MM patients and provide the rationale for clinical evaluation of HIF inhibitors. Disclosures: No relevant conflicts of interest to declare.

Description: Abstract 861 The high rate of complete response (CR) effected by novel agents as induction and consolidation/maintenance therapy in multiple myeloma (MM) has renewed interest in the evaluation of minimal residual disease (MRD) after these combined treatment strategies. For this purpose, a useful molecular marker is represented by the immunoglobulin heavy-chain (IgH) rearrangement which can be carefully detected by means of polymerase chain reaction (PCR). We designed a molecular sub-study to the phase 3 GIMEMA trial of bortezomib-thalidomide-dexamethasone (VTD) vs. thalidomide-dexamethasone (TD) incorporated into double autologous stem cell transplantation (ASCT) for newly diagnosed MM. By study design, patients randomized at diagnosis to VTD or TD as induction therapy before ASCT received two 35-day cycles of consolidation therapy with VTD or TD starting 3 months after ASCT(s), independently from prior response. Doses of study drugs were the following: V, 1.3 mg/m2 once weekly; T, 100 mg/d through d 1 to 70; D, 320 mg/cycle. Aim of the molecular study was to compare the activity of VTD consolidation with that of TD by qualitative and quantitative PCR analysis. Patients who were planned to receive consolidation with either VTD or TD and who were in confirmed CR or near CR before the start of consolidation therapy were eligible for entry into the molecular study. A qualitative and quantitative PCR analysis with patient-specific primers was performed on bone marrow samples collected at day 0 and at day +70 after the two preplanned cycles of either VTD or TD. At this time, 84 patients were included in the study; of these, 67 patients were analyzed for MRD detection based on the availability of: 1) a molecular marker (e.g. IgH rearrangement) assessed at diagnosis; 2) both pre- and post-consolidation bone marrow samples. According to randomization at diagnosis, 35 out of 67 patients received VTD consolidation, while TD consolidation was given to 32 patients. Qualitative PCR analysis performed on bone marrow samples collected at day 0 showed that MRD before the start of VTD consolidation therapy was undetectable in 15 out of 35 patients, or 43%; the corresponding value before the start of TD consolidation was 37.5% (or 12 out of 32 patients). In comparison with the pre-consolidation status, analysis of bone marrow samples collected at day +70 revealed an upgrade in PCR-negativity from 37.5% to 52% with TD consolidation and from 43% to 67% with VTD consolidation (p=0.05, according to McNemar's test). By using the Fisher's exact test, the proportion of patients with post-consolidation PCR-negativity was significantly higher with VTD vs. TD consolidation (p=0.05). These data were furtherly extended by a Real-time quantitative PCR analysis, which could be performed in 45 out of the 67 patients initially included in the study (22 in the TD arm and 23 in VTD). In comparison with residual tumor mass at day 0, quantitative PCR analysis of bone marrow samples collected at day +70 revealed a median 1 log reduction in tumor burden with TD consolidation vs. a median 5 log reduction with VTD consolidation. By using the Wilcoxon test, the overall reduction in residual tumor burden effected by VTD consolidation therapy was statistically significant (p=0.05). In conclusion, in comparison with TD consolidation, two 35-day cycles of consolidation therapy with VTD following double ASCT significantly increased the rate of molecular remissions and significantly reduced the burden of residual myeloma cells persisting after ASCT. Superior activity of VTD over TD consolidation was retained although prior exposure to the same regimen given as induction therapy in preparation for ASCT. Additional data on molecular follow-up analyses of bone marrow samples collected after day +70 and comparisons of the prognostic relevance of PCR-negativity with PCR-positivity, as well as of PCR-negativity induced by VTD with that induced by TD will be presented during the meeting. Supported by: Progetto di Ricerca Finalizzata Orientata (to M.C), BolognAIL, Fondazione del Monte di Bologna e Ravenna. Disclosures: Baccarani: NOVARTIS: Honoraria; BRISTOL MYERS SQUIBB: Honoraria. Cavo:jansen-cilag: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau, no; celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau, no; novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau, no.

Description: Introduction The differentiation status plasticity of Multiple Myeloma (MM) plasma cells (PCs) is an adaptive strategy that might confer a specific fitness to tumour cells, enabling their interaction with an evolving microenvironment. Therefore, proliferation rates of MM clones are not constant, and the immunophenotypic profile of the most skilled MM PCs might be the expression of specific genetic and genomic programs, that emerge under the therapeutic pressure and promote tumour development. However, the genomic background that supports any diverse plasma cell differentiation phenotypes has not yet been inferred. Aim To correlate the genetic and genomic background with the immunophenotypic profile of MM clones at diagnosis, in order to stratify patients (pts) according to a Maturation Index, and ultimately to evaluate the impact of this stratification on the disease outcome. Patients and Methods 117 newly diagnosed MM (NDMM) pts, mostly treated up-front with a proteasome inhibitor (PI) -based treatment, were included in the study. For each pts, both neoplastic PCs and CD19+ B cells compartments were characterized by 8-color multi-parameter flow cytometry analysis, combining CD138-PE, CD38-PE-Cy7, CD56-APC-Cy7, CD20-APC, CD19-FITC, CD27-APC, CD45-PerCp, CD28-APC, CD117-FITC, CD28-APC, CD81-APC, IgK-APC and IgL-FITC. In a subgroup of pts, both a SNP array profile for copy number alterations (CNAs) and a 25-genes targeted mutational panel were assessed in CD138+ PCs. A custom ddPCR assay was also employed to evaluate through a 10-Hh gene signature the self-renewal status of PCs. Results In order to define a Maturation Index, pts were evaluated at different levels of heterogeneity for: a) differential expression of CD19/CD81 markers; b) level of chromosomal instability (CIN) and point mutations; d) self-renewal status. Based on the co-expression of CD19 and CD81 markers, pts were stratified in 3 different subgroups, recapitulating a progressive PC maturation process: the most immature, which included pts with CD19+/CD81+ PCs (18/117 = 15%), the intermediate, including CD19-/CD81+ PCs (42/117 = 36%) and the most mature, including CD19-/CD81- PCs (57/117 = 49%). The advanced PC differentiation status characterizing this latter subgroup was further confirmed by the high expression of CD28 and CD44, and the reduced expression of CD20, CD27 and CD45, commonly associated with less mature stages of the disease (p

Description: In Multiple myeloma (MM) no treatment has a curative potential and even complete response to novel agents such as proteasome inhibitors (PIs) and immunomodulatory agents (IMiDs) are followed by relapse over time. Next generation sequencing (NGS) has showed how MM at diagnosis is defined by several somatic mutations, but only few drivers, even fewer "druggable" mutations, and many found at a subclonal level. At relapse, targeted studies have shown occasional mutations in drug target genes but the genomic and transcriptomic determinants of chemoresistance in MM remains elusive. We selected 42 MM patients refractory to both lenalidomide and PIs. Whole exome sequencing was performed in 40 of them, and RNAseq in 27. Clinical annotation was available for all patients. Standard analysis pipelines where applied to analyze mutations, copy number alterations (CNAs), mutational signatures, gene expression and expressed mutations. Patients received a median of 3 lines of treatment, with median overall survival of 14.6 months from sampling. We found a median of 77.5 mutations per patient, which is more than what reported at diagnosis (Bolli et al, Nature Communications 2014;5:2997). 100% of samples showed evidence of subclonality, and 37% of them exhibited a higher number of subclonal than clonal variants. Therefore, even at this advanced stage the MM genome is evolving and is composed of different subclones that may display different chemosensitivity. The mutational landscape was also different. TP53 mutations were the second most common after KRAS (20% and 17.5%, respectively). Interestingly TP53 mutations all clustered in patients receiving bortezomib as the last line of treatment. Only 2 patients showed a CRBN mutation, both subclonal. Combining mutations and CNA analysis, the TP53 pathway was the most frequently inactivated (45% of patients). Altogether, mutations or deletions of genes in the CRBN E3 ubiquitin ligase complex were found in 32.5% of patients, while proteasomal subunit genes were infrequently hit. Refractory cases were also uniquely characterized by a novel signature linked to exposure to alkylating agents, whose activity was more pronounced after high-dose melphalan suggesting a mutagenic effect of the drug on residual cells at the time of transplant. Whether this has any pathogenetic role on the disease course remains to be elucidated. RNAseq analysis did not show any influence of treatment or mutational data on the clustering of samples, which was mainly influenced by karyotypic events. The main cluster was composed by non-hyperdiploid patients with both amp(1q) and del(13): these showed CCND2 and MCL1 upregulation, the latter representing a marker of venetoclax resistance and novel target of experimental treatments. Only 26.3% of mutations were expressed, and this correlated with the clonality level of the mutation. However, most mutations in driver genes were expressed, with the notable exception of those causing nonsense mediated decay. Overall, classical high-risk features or CRBN pathway mutations were found in 65% of the cohort. However, only amp(1q) predicted survival in our cohort. The lack of prognostic value of high-risk lesions is likely explained by a higher prevalence of such features in double-refractory stages. Our data suggest that gene mutation is not a preferred mode of evolution of drug resistance in MM. Chemoresistance of the bulk tumor population is likely attained though differential, yet converging evolution of different subclones that are overall highly variable from patient to patient and within the same patient. Disclosures Kastritis: Prothena: Honoraria; Genesis: Honoraria; Amgen: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Takeda: Honoraria; Pfizer: Honoraria. Dimopoulos:Sanofi Oncology: Research Funding. Cavo:bms: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accommodations, Speakers Bureau; sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; novartis: Honoraria; takeda: 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 accommodations, Speakers Bureau; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Corradini:Janssen: Honoraria, Other: Travel Costs; Takeda: Honoraria, Other: Travel Costs; Jazz Pharmaceutics: Honoraria; Gilead: Honoraria, Other: Travel Costs; Daiichi Sankyo: Honoraria; Celgene: Honoraria, Other: Travel Costs; Amgen: Honoraria; AbbVie: Consultancy, Honoraria, Other: Travel Costs; KiowaKirin: Honoraria; Kite: Honoraria; BMS: Other: Travel Costs; Sanofi: Honoraria; Servier: Honoraria; Roche: Honoraria; Novartis: Honoraria, Other: Travel Costs. Bolli:Celgene: Honoraria; Novartis: Honoraria; Gilead: Other: travel expenses.

Description: Multiple Myeloma (MM) maintenance therapy is a low intensive, prolonged treatment, commonly administered to newly diagnosed patients (pts) at the end of fixed-time, front-line regimens. Lenalidomide (LEN) is considered the best available maintenance option for MM able to prolong pts survival. However, the actual benefits or disadvantages of a LEN-based continuous maintenance and its potential role as selective pressure able to induce genomic changes are still unclear. The identification of specific therapy-driven modifications has been so far prevented by the scarce number of homogeneously-treated cohorts of pts with paired samples (diagnosis, D and relapse, R). In this study we estimated the role of LEN maintenance therapy in eliciting genomic changes in a cohort of MM pts homogeneously up-front treated with PI-based regimens. Whole genome Copy Number Aberrations (CNAs) landscape was obtained by SNPs array in 54 pts whose BM-CD138+ were collected both at D and at first R. Pts had an high-risk (HR) disease, as defined both by the presence of HR cytogenetic aberration at baseline in 81% of pts and by the 29 m median TTP. RawCopy 1.10 was used for the segmentation of SNPs array signals; samples' purity was adjusted by using manually reviewed ASCAT solutions. A custom gene-level CN calling approach was set up, to match every gene's CN value at D and R, thus generating genomic evolutive patterns based on changes of these values. Finally, high-risk genomic loci were computed using GISTIC 2.0_v7 to derive focal regions with oncogene and/or tumor suppressor genes relevant for MM biology. After induction therapy, 31/54 pts were treated with HD chemotherapy followed by either single or double ASCT; LEN maintenance therapy was then offered both to 20/31 auto-transplanted and to 6/23 not auto-transplanted pts. Three main evolutive trajectories (linear L, drift D, and branching B) were defined according to the CN changes' direction, reflecting a putative positive, negative, or both positive and negative selective pressure, respectively. A fourth, stable (S) trajectory was also observed, characterized by the absence of CN changes between D and R. Overall, 29, 15 and 10 pts relapsed with B/D, L and S pattern, respectively; at R, all LEN-treated pts quantitively and qualitatively changed their sub-clonal architecture: a B/D evolutive pattern characterized 70% of pts. By contrast, genome remained mostly stable in 61% of not-treated pts. We then focused on CN changes of specific chromosomal regions and/or genomic loci, whose prognostic role has been already established in MM (i.e. CN losses of TP53 on chr17p, RB1 on chr13q, CYLD on chr16q, CDKN2C and FAM46C on chr1p; CN gain of CKS1B on chr1q). When present at D these CNAs tended to persist throughout the disease course regardless of whether pts received or not maintenance. The emersion of any of these CNAs at R was widely observed both in pts receiving or not maintenance, whereas a negative selective pressure over them was more likely to occur in pts receiving maintenance, as compared to the others (50% vs 11% of B/D trajectories in LEN-treated vs not-treated pts, respectively). Strikingly, in LEN-treated pts, the extension of both TTP and OS was favored by the extinction and/or negative selection of the HR CNAs (B/D patterns), and shortened by their stability or positive selection (L/S patterns) (median TTP 46 vs 32 m HR=3,6 CI 1,2-10,6, p=0.01; median OS 111 vs 63 m HR 5,7 CI 1,1-32,4, p=0.04 in B/D vs L/S pts, respectively). On the contrary, the absence of maintenance selective pressure seemed to affect neither the evolution trajectory, nor the clinical course of not-treated pts (fig 1). The extinction of sub-clones carrying HR lesions in pts receiving maintenance therapy is likely to be associated to the negative selection exerted by the therapy itself. This might explain the extended survival of pts receiving maintenance and relapsing with B/D evolution patterns, as compared to that of pts whose genomic landscape either tended to remain stable or let the prevalent emersion of HR genomic features. On the contrary, the sub-clonal architecture of pts not receiving maintenance seemed to randomly evolve, due to the absence of a specific therapy-related selective pressure. Overall, information on the genomic changes occurring throughout the disease course might be relevant for the recognition of pts most benefitting from a continuous therapy. Thanks to AIRC_IG2014-15839, RF-2016-02362532 Disclosures Zamagni: Takeda: Honoraria, Speakers Bureau; Sanofi: Honoraria, Other: Advisory Board, Speakers Bureau; Janssen: Honoraria, Other: Advisory board, Speakers Bureau; Amgen: Honoraria, Other: Advisory board, Speakers Bureau; BMS: Honoraria, Other: Advisory Board, Speakers Bureau; Celgene Corporation: Honoraria, Other: Advisory board, Speakers Bureau. Tacchetti:BMS: Honoraria; Takeda: Honoraria, Speakers Bureau; Janssen: Honoraria; Oncopeptides: Honoraria, Speakers Bureau; Amgen: Honoraria, Speakers Bureau; Celgene: Honoraria, Speakers Bureau. Mancuso:Celgene: Honoraria, Speakers Bureau; Janssen: Honoraria; Takeda: Honoraria; Amgen: Honoraria. Petrucci:Janssen-Cilag: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: 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; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees. Liberati:Incyte: Consultancy; Servier: 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; Takeda: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Bristol & Mayer: Honoraria; Janssen: Honoraria; Celgene: Honoraria. Rossi:Roche: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Daiichi-Sankyo: Consultancy; Celgene: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Jazz: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria; Mundipharma: Honoraria; BMS: Honoraria; Sandoz: Honoraria. Boccadoro:Bristol-Myers Squibb: Honoraria, Research Funding; Mundipharma: Research Funding; Sanofi: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Amgen: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; AbbVie: Honoraria. Cavo:amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; novartis: Honoraria; sanofi: 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; janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accommodations, Speakers Bureau; celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accommodations, Speakers Bureau; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees.

Description: Background Multiple Myeloma (MM) is a biologically complex disease, whose genetic plasticity favors the coexistence of genetically heterogeneous subclones, selected in a Darwinian fashion throughout the disease course. Based on a disease evolution model, it is likely that therapy acts like an evolutionary bottleneck, applying a selective pressure on the clones' genomic background. However, a formal correlation between the modulation of intra-clonal heterogeneity and the treatment has yet to be demonstrated. Aim To explore the existence of different clonal evolution patterns in MM, eventually driven by therapeutic selective pressure, we longitudinally analyzed a cohort of patients (pts) by using a high-throughput technology, able to finely dissect the genomic intra-clonal changes occurring in each pts, across disease progression. Patients and methods Thirty-three pts with symptomatic MM were included in this study. Most pts (28) were up-front treated with regimens including a proteasome inhibitor (PI), either in combination with an immunomodulator (IMiD) (thalidomide or lenalidomide) or with cyclophosphamide. The remaining pts (5) were up-front treated with IMiDs-based regimens, not including PI. For each pts, paired bone marrow samples were collected both at diagnosis and at relapse. SNPs array analyses were performed on the CD138+ enriched cell fractions (Affymetrix 6.0 and CytoscanHD) and data were analyzed with ChAS v3.1 and Nexus software, to obtain Copy Number Alterations (CNAs) results. Results: The genomic landscape's modulations were evaluated in details in each pair of samples included in the study: by one side, by monitoring the variations of macro CNAs types; by the other, by focusing on changes of CNAs frequencies, as observed in 27 genes of interest (selected according to their recognized role in MM pathogenesis). Both approaches were consistent in highlighting three major evolution patterns: in 7/33 (21%) pts, the genomic background at relapse was almost identical to that of diagnosis, suggesting that no evolution affected the diagnosis' genomic architecture. In 13/33 (39%) pts, an overall increase in the frequencies of the same CNAs as observed at diagnosis was detected at relapse, suggesting a linear evolution of the diagnosis' predominant clone. Finally, in 13/33 (39%) pts, either increased or decreased frequencies of several CNAs, as well as several differences in the CNAs type's prevalence were observed in samples collected at relapse, as compared to those collected at diagnosis, suggesting a branching evolution of sub-clones not-detectable at diagnosis. Of interest, even if an overall increase in the median number of CNAs was observed in the CD138+ cell fractions collected from the whole population of newly diagnosed and relapsed pts (226 vs 507, respectively) - supported by acquisition of CNAs either commonly described as secondary genomic events (i.e. del17p13, amp1q21, del1p23), or associated to the resistance to bortezomib (i.e. del8p21) - nevertheless any peculiar CNAs resulted significantly prevalent in the three identified subgroups of pts. The subgroup of pts who underwent a branching evolution was characterized by a high rate (92%) of achievement of VGPR or better quality of response to upfront therapy, regardless of incorporation of PI into induction regimens. On the contrary, although pts who experienced either linear or no evolution were mostly treated with highly effective PI-based triplet combinations (19/20 pts), the rate of VGPR in this subgroup was only 20% and PR or SD were observed in 9 and 7 pts, respectively. Finally, the median time to first progression of this subgroup of pts was significantly shorter as compared to that of pts with branching evolution (24 vs 35 months, range 4-41 and 7-123 months, respectively, p=0,01). Conclusion The genomic architecture of a subgroup of relapsed MM pts, who were up-front responsive to new drugs-based combination therapies, resulted overall different from that of diagnosis, suggesting a branching evolution of the disease, sustained by the shrinking of the most prevalent clone (therapy-sensitive), as well as by the expansion of subclones (therapy-resistant) not already evident at diagnosis. This observation raises the question whether re-treatment of relapsed pts should be appropriate in the case of branching evolution. Acknowledgments: AIRC (MC), Fondazione Berlucchi (CT), FUV (EB). Disclosures Cavo: Takeda: Honoraria; Amgen: Honoraria; Bristol-Myers Squibb: Honoraria; Celgene: Honoraria, Research Funding; Janssen: Honoraria, Research Funding.