Barrio, Santiago

Abstract Introduction: Monoclonal B cell lymphocytosis (MBL) is an asymptomatic expansion of clonal CD19+/CD5+ B cells with less than 5x109/L cells in the peripheral blood and without other manifestations of chronic lymphocytic leukemia (CLL). Approximately 1% of MBL evolves to CLL requiring therapy per year; thus it is critical to develop more precise tools to identify which MBL will progress to CLL and require treatment. Patients and Methods: In this study, we performed targeted deep sequencing (TDS) on 49 high-count MBL individuals (median B-cell count 3.7x109/L; range 0.8-4.9x109/L) and explored the mutation status of 20 driver genes recurrently mutated in CLL. We analyzed the clonal evolution in 45 of these 49 MBLs by screening 2-4 sequential samples (average time between samples 56 months, range 10-119 months). At last follow-up, 19 cases (39%) had progressed to Rai>0, and 10 cases (20%) required treatment. Tumor and germ line DNAs were isolated from sorted CD5+/CD19+ and CD5-/CD19- cell populations, respectively. Overall, 154 samples from 49 MBL cases (105 tumor and 49 germ line) were screened using semiconductor sequencing technology. The latter genetic information was integrated with relevant clinical and biological parameters, and we evaluated the effect of driver mutations and clonal expansion on time to CLL progression and time to treatment (TTT). Results and Discussion: Our cohort consisted in 17 women and 32 men, with a median age of 66 years (range: 44-80). Five cases presented secondary diseases, including melanoma, lung and bladder cancer. Clinical and biological parameters were collected, including IGHV mutation status (mutated 66%, unmutated 34%), ZAP70 and CD49 expression (25% each). At presentation, 46% of cases had del(13q), 27% trisomy 12, 6% del(11q), and 4% del(17p). Overall, we found somatic non-synonymous mutations in 23 of 49 MBLs (47%) at the initial time point including 22% of cases with more than one mutated driver gene. The average depth of coverage was 730x, thus allowing the identification of small subclonal mutations. Recurrent mutations were found in most of the drivers: CHD2, DDX3X (8% of cases), FBXW7, NOTCH1, SF3B1 (6% each), ATM, BCOR, BIRC3, BRAF, KRAS, MED12, MYD88 and ZMYM3 (4% each). Furthermore, ITPKB, POT1, SAMHD1 and XPO1 were mutated in only one case, whereas no mutations were found in HIST1H1E, RIPK1 and TP53. In 4 individuals, we found two mutations in the same gene (BRAF, DDX3X, KRAS and SAMHD1). Genes that are known to be associated with disease progression in CLL were either mutated with significantly lower incidence (NOTCH1, SF3B1) or not mutated (TP53). Mutations were detected on average 45 months (range 9-73) prior to progression to CLL Rai>0 indicating the early origin of most driver gene mutations in the MBL/CLL continuum. The presence of driver mutations in MBL was associated with shorter TTT (median TTT: present: 96 months vs. not present: not reached, HR: 5.52, 95% CI: 1.2-26.2, P =0.015). Next, we looked at clonal expansion of driver mutations over time (defined as >2-fold change in the allelic frequency of driver mutations between time points). Of 20 MBLs with mutations at baseline who had sequential samples available, 10 cases showed clonal expansion. Seven out of 10 MBLs who required therapy showed clonal expansion, which was detected on average 15 months (range 6-30 month) prior to treatment. Finally, the detection of clonal expansion was significantly associated with reduced TTT (median TTT: clonal expansion: 21 months vs. no clonal expansion: 84 months, HR: 7.79, 95% CI: 1.94-31.3, P <0.001). Conclusion: We have confirmed the existence of recurrent mutations in most CLL putative driver genes at the premalignant MBL stage many years before progression to CLL. Furthermore, the early identification of driver mutations and its clonal expansion predicts a shorter TTT. Of note, clonal evolution under selective pressure has recently been linked to the onset of CLL progression after therapy. In this study, we characterized the clonal dynamics in the pre-malignant stages of the disease and underlined its impact on clinical outcome. Despite the relatively small size of the cohort, these findings suggest that the sequential monitoring of MBL individuals with a simple and reliable technique, such as TDS, will be at least of prognostic use and thus its incorporation in the disease stratification and clinical management should be further tested. Disclosures Fonseca: Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Applied Biosciences: Membership on an entity's Board of Directors or advisory committees; Sanofi: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Millennium: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Binding Site: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Onyx/Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Bayer: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding. Kay:Gilead: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmacyclics: Research Funding; Tolero Pharma: Research Funding; Genentech: Research Funding; Celgene Corporation: Membership on an entity's Board of Directors or advisory committees, Research Funding; Hospira: Research Funding.

Abstract Introduction: We employed a customized Multiple Myeloma (MM) specific Mutation-Panel (M3 P) to screen a homogenous cohort of refractory MM (rMM) patients in a timely and cost-effective manner. rMM was defined as progressive disease (PD) during therapy or within 60 days after discontinuation of therapy. The M3 P provides a practical alternative to whole genome/exome sequencing approaches and includes 88 genes selected for being either actionable targets, potentially related to drug response or part of known key pathways in MM biology. Patients and Methods: Tumor and germline samples of 50 rMM patients were screened using M3 P. Patients received a median of five lines of treatment at the time of tumor sampling (range 2-15 lines). All patients received at least one immunomodulatory agent (IMiD) and proteasome inhibitor (PI), and 88%, 76% and 66% were refractory to either an IMiD, PI or both. All patients had received lenalidomide and bortezomib, 48% and 34% were additionally exposed to pomalidomide and thalidomide and 18% to carfilzomib at any time prior to sampling. The majority of patients had a progressive and refractory disease immediately prior to sampling (82% and 78%), with 43% of them being IMiD-refractory and 46% being PI-refractory in the most recent line of therapy. Cytogenetic data at time of sampling were available from 78% of patients. Adverse cytogenetics were detectable in 82% of patients with gain 1q21 > 2 copies (62%), deletion 17p (33%), t(4;14) (13%) and t(14;16) (8%) being the most common. Results: An average sequencing depth of 750x was obtained across the samples. Our screening revealed an increased prevalence of mutations in the MAPK pathway (72%), including 34% of KRAS, 26% of NRAS, 18% of BRAF (with one patient carrying two BRAF mutations and 8% in actionable p.V600E). Additionally, two mutations (4%) were found in RASA2, a RAS inhibitor. Other potentially actionable mutations were seen in p.R132H IDH1 and p.R248C FGFR3 (2% each). Most prominently, the CRBN pathway was found mutated in 22% of cases, including CRBN (12%, one case with concomitant CUL4B mutations), CUL4B (4%), IRF4 (4%) and IKZF1 (2%). In CRBN we found four cases with mutations leading to a truncated protein (frameshift, nonsense and splicing) and two cases with missense mutations located within the thalidomide-binding domain, suggesting a causal effect on IMiD resistance. All CRBN mutated patients and 91% of the CRBN pathway mutated patients were at least once unresponsive to IMiD based treatment. In one patient with IRF4 mutation sensitivity to IMiDs remained unknown. A majority of patients were also resistant to PI treatment (76%), however mutations in proteasome subunits (PSMD1 and PSMB8) and XBP1 wererare (4%), but only a limited number of this gene family were represented in our panel. Other recurrently mutated genes were TP53 (26%), FAM46C (12%), ATM (10%) and TRAF3 (8%). Notably, DIS3 mutations were identified in only 6% of cases. As previously reported, TP53 mutations were associated with deletion 17p (8/13 cases, 62%). A correlation between the absolute number of mutations and previous lines of treatment was not observed (r=0.05, p=0.73). Conclusion: Targeted sequencing on a homogenous cohort of heavy pretreated rMM patients gives key insights in the landscape of the rMM genome, uncovering an increasing frequency of MAPK, TP53 and CRBN mutations. Importantly, this is the first study showing recurrent mutations in CRBN in patients unresponsive to IMiD treatment, supporting a potential association with resistance to IMiD based therapies. Disclosures Mai: Onyx: Other: Travel Grant; Janssen-Cilag: Other: Travel Grant; Celgene: Other: Travel Grant; Mundipharma: Other: Travel Grant. Merz:Janssen: Other: Travel grants; Celgene: Other: Travel grants. Hillengass:Takeda: Honoraria, Other: Travel support; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi: Research Funding; Janssen-Cilag: Honoraria, Other: Travel support; Celgene: Honoraria, Other: Travel support. Goldschmidt:Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Janssen-Cilag: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Millennium: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Onyx: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Chugai: Research Funding, Speakers Bureau. Stewart:Oncospire Genomics: Research Funding.

Abstract BACKGROUND: The first step to the cure of Multiple myeloma (MM) is achieving a clinical complete response (CR). However, a majority of patients relapse in part due to the persistence of low levels of pathological plasma cells after treatment (minimal residual disease (MRD)). In previous work, we have shown that Next generation sequencing (NGS) of immunoglobulin (IG) rearranged genes is an effective technology to identify and quantify pathological clonal cells in MM, and also it is a good predictor of patient prognosis. However, this technology is a proprietary multiplex PCR, uses a reference plasmid, it is performed at the centralized laboratories, and it is not broadly available. AIMS: To present a new in-house simplified method for quantification of IG gene clonal rearrangements by NGS. To test the suitability of the method for MRD detection in MM patients compared with 8-color high sensitivity Flow Cytometry (8c-MFC) data on a prospective way. To determine its capability as a predictor of patient prognosis. METHOD: We use deep sequencing to prospectively analyzed DNA from bone marrow samples of 58 patients (58 diagnostic samples and 80 follow-up samples) of patients included the GEM10 clinical trial. The method employs the primers developed by BIOMED-2 for IGH and IGK, and a set of specific mathematical and bioinformatics tools. First, we identified the clonal rearrangement(s) (clonotype) in the diagnostic sample by fragment analysis and NGS. Second, we searched the NGS sequences from follow-up samples to detect and quantitate (MRD) the presence of the clonotype identified in the diagnostic sample. Overall Survival (OS) and Progression free Survival (PFS) were estimated by Kaplan-Meier survival analysis. The survival curves generated were compared with the log-rank test for trend. RESULTS: The sensitivity of the method is 10-5 for 150.000 cells. Reproducibility is >90%. The Spearman correlation coefficient between NGS and 8c-MFC data for diagnosis and follow-up samples was R=0.6903, p<0.0001. When we applied the criteria of 10-5 for NGS, discordant results were as follow: 121 cases were positive by both methods, 2 cases were positive (>10-5) by 8c-MFC but negative (<10-5) by NGS; 7 samples were negative (<10-5) by 8c-MFC but positive (>10-5) by NGS; and 7 cases were negative by both methods. Next we analyzed de correlation of OS and PFS with MRD levels determined by NGS and by 8c-MFC. For NGS data, median PFS (FigA) was 34 months for patients with values of MRD>10-5 vs not reached for patients with values of MRD<10-5 (hazard ratio [HR] = 3.69, P =0 .0109). Also, for 8c-MFC data, the patients with values of MRD<10-5 had longer PFS than those with values of MRD>10-5 (34 months versus 47; HR = 3.69, P =0 .0109). Median OS (FigB) was also significantly longer in MRD<10-5 (NGS) patients (not yet reached), compared to MRD>10-5 (NGS) patients (41 months, HR = 3.6, P =0.0495). For 8c-MFC we did not get a significant association (41 vs 50 months, HR=1.979, p=0.228). It should be noted that this comparison was made with the standard 8c-MFC and it is probable that the sensitivity will be inferior to that of the Next generation flow. There were no significant differences in terms of PFS between the data obtained by our in-house method, 8c-FCM and previous data obtained with LymphoSight technology. CONCLUSIONS: Our data confirms that analysis of MRD levels determined by deep sequencing is capable of predict survival outcomes in myeloma patients. NGS sequencing of Ig genes is an effective technology to identify and quantify pathological clonal cells in MM. This approach is a methodological and economical alternative to MFC and other methods for MRD follow-up. Figure 1. Figure 1. Disclosures Paiva: Janssen: Consultancy; Celgene: Consultancy; BD Bioscience: Consultancy; Sanofi: Consultancy; Binding Site: Consultancy; Onyx: Consultancy; Millenium: Consultancy; EngMab AG: Research Funding. Ocio:Pharmamar: Consultancy, Research Funding; MSD: Research Funding; Novartis: Consultancy, Research Funding; Mundipharma: Consultancy, Research Funding; Bristol Myers Squibb: Consultancy; Amgen/Onyx: Consultancy, Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Array BioPharma: Consultancy, Research Funding; Jassen: Honoraria. Mateos:Celgene: Consultancy, Honoraria; Takeda: Consultancy; Janssen-Cilag: Consultancy, Honoraria; Onyx: Consultancy. San Miguel:Novartis: Honoraria; Celgene: Honoraria; Janssen-Cilag: Honoraria; Bristol-Myers Squibb: Honoraria; Millennium: Honoraria; Onyx: Honoraria; Sanofi-Aventis: Honoraria.

Abstract Introduction: Customized gene panel sequencing is an attractive approach to genomic tumor characterization in clinical care. Based on published MM exome data we developed a MM Mutation Panel (M3 P) that includes the most commonly mutated genes, actionable drug targets, genes targeted by current standard of care (SOC) therapies and which allows tracking of clonal evolution, copy number and sample purity. Methods and Material: M3 P (v3.0) covers 88 genes (1327 amplicons, 181kb). MM samples from 504 patients (pts) have been analyzed (corresponding germline in 81%) through collaborations between Mayo Clinic and Hospital-12-de-Octubre (Madrid, Spain), the DSMM and GMMG (Würzburg, Ulm, Freiburg and Heidelberg, Germany) and the HOVON trial groups (Rotterdam, The Netherlands). The investigated cohort includes 410 untreated pts (81%), which includes a high risk cohort of 72 pts with del17p, 25 paired samples with later follow up from the same cohort, and 94 relapsed patients, of which 50 were relapsed and refractory. Results: Overall coverage per mutation averaged >500x depth. We identified 945 variants (1.9 per pt) and in 83% of the pts a mutation was found. Clonal heterogeneity was assessed with mutations ranging from 3%-100% variant reads suggesting the presence of a significant number of subclones (e.g. 21% of mutations were in < 10% of reads). The mutation incidence was compared with and closely resembles the most recent MM comprehensive genomic data from the MMRF CoMMpass study: We compare here all pts sequenced by M3 P, untreated pts sequenced by M3 P and CoMMpass: KRAS (24%/23%/24%), NRAS (20%/20%/18%), DIS3 (13%/14%/10%), BRAF (9%/7%/6%), FAM46C (6%/6%/8%) and TRAF3 (6%/6%/7%). TP53 mutation incidence, however, was significantly increased in our cohort (14%/12%/4.2%), a difference explained by the inclusion of del17p (untreated) and relapsed refractory MM in panel sequenced pts, cohorts with elevated incidences of TP53 mutations (32% / 26% respectively). Potentially actionable targets include BRAF mutationsin 43 patients (9%), with druggable p.V600E in 19 or 5%, 8 pts (2%) with FGFR3 (p.R248C and p.G375C one patient each), p.R132 mutation in 4 out of 5 IDH1 (1%) and p.R172K IDH2 mutation in 1 of 3 (1%) pts. Mutations in the MAPK pathway (NRAS, KRAS, BRAF) were detected in 59% of pts, ranging from 36% untreated MM to 72% in refractory MM. Similarly, the CRBN/CUL4B/IKZF1/IKZF3/IRF4 pathway, important for IMiD function, harbored a significant enrichment of mutations in advanced disease (6% untreated vs 17% relapsed), including CRBN mutations (0.5% vs 7%). Nine of 17 IRF4 mutations were located at the p.K123R hotspot, with minor difference between early or late disease (1% vs 3%). Notably, in 8 of 9 pts with CRBN mutation and clinical information, all were unresponsive to IMiD therapy, supporting association of these mutations with resistance to IMiDs. Conversely, M3 P genes related to other SOC therapies, including NR3C1 (targeted by steroids) and 5 proteasome subunit genes (proteasome inhibitors), were rarely mutated across the cohorts not exceeding 1% mutation incidence for each gene. Significant differences in DIS3 and FAM46C mutation incidences were observed across cohorts: DIS3 mutations are more common in untreated pts with a 1.7 fold increased predominance (14% untreated and 8% treated). FAM46C has an expected incidence of 8% but was rarely mutated in untreated del17p high risk disease with only one of 100 patients harboring both mutations. The significance of this finding needs to be determined but implies a possible overlap in function. Finally we assessed impact on survival of the mutation variants identified in 142 untreated Mayo patients and found STAT3 mutations negatively impacting PFS (p=0.034) and OS (p=0.001). This gene is rarely mutated in MM (2% of the total cohort) thus the sample size was small and this finding needs further validation. Conclusion: We here describe 504 MM patients sequenced using the M3 P gene panel, which identified mutations in >80% of investigated patients, overlaps well with published whole exome sequence data and provides clinically relevant information. New findings were the high frequency of minor clones, the relative lack of overlap of del17 and FAM46C mutation, a higher frequency of DIS3 mutation at diagnosis compared to relapse, the prognostic significance of STAT3 mutation and the frequent presence of CRBN pathway mutation in drug resistant relapsed patients. Disclosures Sonneveld: Janssen-Cilag, Celgene, Onyx, Karyopharm: Honoraria, Research Funding; novartis: Honoraria. Mai:Janssen-Cilag: Other: Travel Grant; Onyx: Other: Travel Grant; Mundipharma: Other: Travel Grant; Celgene: Other: Travel Grant. Goldschmidt:Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Onyx: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Millenium: Honoraria, Research Funding, Speakers Bureau; Bristol-Myers Squibb: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Chugai: Honoraria, Research Funding, Speakers Bureau; Janssen-Cilag: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Knop:Celgene Corporation: Consultancy. Kull:Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees. Martinez-Lopez:Novartis: Honoraria, Research Funding; Bristol-Meyer Squibb: Honoraria; Celgene: Honoraria; Janssen: Honoraria. Einsele:Celgene: Consultancy, Honoraria, Research Funding, Speakers Bureau; Janssen: Consultancy, Honoraria, Research Funding, Speakers Bureau; Novartis: Consultancy, Honoraria, Speakers Bureau; Amgen/Onyx: Consultancy, Honoraria, Speakers Bureau. Raab:Novartis: Research Funding. Stewart:Oncospire Inc.: Equity Ownership; Celgene: Consultancy; Novartis: Consultancy; BMS: Membership on an entity's Board of Directors or advisory committees.

Abstract Background. The AML is a heterogeneous disease with a high variety of subtypes stratified by cytogenetic and molecular markers. To date, the major prognosis criteria is cytogenetic, but 40-50% of de novo AML patients have normal karyotype; AML treatment is based on risk profiles depending on age and genetic molecular factor. New methods such as Next Generation Sequencing (NGS) and ex vivo sensitivity drug tests might be able to improve this classification and to individualize the treatment for AML patients. Aims. We performed targeted massively parallel sequencing on a 32 myeloid genes custom panel to identify a mutational profile of AML which predicts ex vivo pharmacological and clinical response. Methods. We analyzed bone marrow (BM) samples at diagnosis from 39 AML patients, 34 were treated with chemotherapy; 28 AML patients received one cycle of Idarubicin (Ida)/ Cytarabine(Cyt) induction treatment (3+7) and 8 received one cycle of Fludarabine/Cyt. Median age at diagnosis was 53 years (24-81), male:female ratio 19:16. We carried out targeted gene sequencing by NGS (Ion Torrent Proton System-Life Technologies) using a 32 genes custom panel (all coding regions) implicated in leukemia prognosis, including ASXL1, CBL, DNMT3A, EPOR, ETV6, EZH2, FLT3, HRAS, IDH1, IDH2, JAK2, KDM6A, KIT, KRAS, LNK, MLL, MPL, NRAS, PHF6, PRPF40B, PTEN, RUNX1, SF1, SF3A1, SF3B1, SRSF2, TET2, TP53, U2AF35, VHL, ZRSR2 and CALR. Ex vivo pharmacological studies were performed using an innovative automated flow cytometry method based platform (Ex-viTech) is able to evaluate effect of drugs used to treat AML, Cyt and Ida, using 4 parameter: Emax (Effective Maximum Response) measures potency, EC50 (Effective Concentration inducing 50% cell death) measures efficacy, and the activity was quantified by AUC (Area Under Curve) and VUS (Volume Under Superficies). Clinical response was evaluated after induction treat. Complete remission was defined according to hematologic recovery and blast count fewer than 5%. Analysis of NGS results was performed by Ion Report software. Differences measured by Exvitech were determined using t-test or Kruskal-Wallis test. Discrete variables of patients with and without gene variants were compared using the X2 test. For survival analysis we used Kaplan-Meier analysis (log rank) using SPSS 15. Two sided p values below 0.05 were considered statistically significant. Results. We found 94 non-synonymous variants (SNVs and small Indels) in coding regions. On average, 90.8% of the target sequence showed mean depth coverage ~ 1100x. See Figure 1. We analyzed results of pharmacological test by Ex-viTech plataform in function of presence of gene variants. Only significant favorable differences were detected: KRAS (Cyt-Emax p=0,000, Ida-EC50 p=0.001, VUS p=0.003, Cyt-AUC p=0.036, Ida-AUC p=0.000), KIT (VUS p=0,010) and FLT3-TKD (Cyt-Emax p=0.002, Cyt-AUC p=0.001, VUS p=0.011). Mutational positive score, found it in 40% of patients, was defined by the presence of variants in KRAS, KIT and/or FLT3-TKD; it was correlated with pharmacological results and clinical response. All cases with positive score (n=13) achieve complete remission (CR); only 11 cases without favorable score (n=21) achieve RC (p=0.003) after induction treatment (See Table 2). In addition, response obtained for Ida Emax and Ida EC50 by Ex-viTech was able to detect patients who reached CR after induction treatment (p=0.042, p=0,039 respectively). Ex-viTech results showed that patients with positive score have a significantly more potent and effective cytotoxic effect than patients without it. See table 2. No differences were observed respect Overall Survival (OS) between cases with mutational favorable score and without it. However, we observed a plateau in OS with favorable mutational score. With a median follow-up of 5.9 months (1.9-25.74), patients having positive score showed better relapse free survival (p = 0.013). See Figure 3. Conclusion. Very deep sequencing NGS identifies a mutational profile score (KRAS, KIT or FLT3-TKD) in AML patients, which predicts ex vivo pharmacological and clinical response. This favorable score was found in 40% of AML patients. Merging NGS and ex vivo drug sensibility might be able early to predict response to induction and individualize treatments. This study was funded by Instituto Carlos III (PI13/02387). Disclosures Ballesteros: Vivia Biotech: Employment.

Abstract Introduction: Proteasome inhibition is the backbone of various Multiple Myeloma (MM) treatment regimens, leading to durable responses and high quality remissions. However, under prolonged therapy patients eventually develop drug resistance and the underlying mechanisms have been poorly understood. Proteasome inhibitor resistant cell lines were generated by continuous exposure to proteasome inhibiting drugs. In these cell line models a number of variants within the PSMB5 gene were observed. This includes single point mutations, leading to conformational changes of the _5 subunit within the 20S proteolytic core of the proteasome, impairing its chymotryptic catalytic function and the binding of inhibitory drugs. However, no PSMB5 mutations could, so far, be identified in human disease, leaving the functional relevance of such mutations to be determined. Methods: We applied the MM Mutation Panel (M3P) and used the Personal Genome Machine (Life Technologies) to sequence CD138+ purified bone marrow plasma cells and peripheral blood germ line control from a MM patient in third relapse that had been previously treated by various proteasome inhibitor containing therapies (VTD-PACE, VCD, PAD-Rev). This patient was subsequently treated with a pomalidomide, bortezomib, adriamycin and dexamethasone combination therapy (Pom-PAD) and achieved a partial remission after 4 cycles of therapy. When being exposed to VCD at earlier relapse a complete remission was induced within 6 cycles of therapy, demonstrating excellent response to proteasome inhibition at this earlier disease stage. Results: We identified clonal missense mutations in this patient at known NRAS hotspot location (p.Gln61Arg) and in MAX (p.Arg35His). Most notably we found and validated four subclonal single point mutations in PSMB5, each of them in subclonal frequencies with variant reads (VR) ranging from 1.9%- 5.9% (average read depth 750X). All PSMB5 mutations occurred in a highly conserved region in exon 2 of the gene (p.Cys122Tyr, p.Met104Ile, p.Ala86Pro, p.Ala79Thr), with three of them being located within the proteasome inhibitor drug binding site. Our 400bp amplicon design allowed us to observe that each mutation identified in PSMB5 is exclusively present on a different sequencing read and no reads are shared between the mutations. This implies that the mutations are present on different subclones of the tumor, which means that, despite low VR frequencies of the single mutation, in sum more than a quarter of the whole tumor might be affected by mutated PSMB5. At a disease stage when the patient was well responsive to proteasome inhibitor treatment (at diagnosis and at first relapse), of note, none of the mutations in PSMB5 is detectable. Conclusion: Here we report the first in human PSMB5 mutation in a MM patient. These mutations evolved in parallel within different subclones of the disease under the selective pressure of bortezomib- containing treatment regimens, representing branching evolution. It is to speculate whether previous investigations negating the existence of PSMB5 mutations in proteasome inhibitor treated patients might not have sequenced deep enough or did set up a sensitivity cut-off too rigid to detect such subclonal mutations. Our finding suggests that the mutations identified may contribute to the development of proteasome inhibitor resistance, emphasizing the need for more detailed genomic characterization of tumors, including minor subclonal mutation detection. Functional analysis of the mutations is ongoing and results will be presented at the meeting. Figure Figure. Disclosures No relevant conflicts of interest to declare.

Progressive multifocal leukoencephalopathy rarely occurs in patients with multiple myeloma. Intracranial central nervous system invasion is also an uncommon event in multiple myeloma, occurring in less than 1% of cases. We describe herein an exceptional case of coexisting progressive multifocal leukoencephalopathy and intraparenchymal central nervous system myeloma infiltration. A 73-year-old woman with relapsed multiple myeloma was treated with 15 cycles of lenalidomide and dexamethasone, but therapy had to be stopped because of a hip fracture after a fall. During hospitalization, the patient developed progressive multifocal leukoencephalopathy caused by John Cunningham virus, and a prominent intra-parenchymal CD138-positive infiltrate was detected. VDJ rearrangements of the immunoglobulin heavy chain gene and the mutational profile of plasma cells in bone marrow at the time of diagnosis and in brain biopsy after progression were analyzed by next generation sequencing, showing genetic differences between medullary and extramedullary myeloma cells. The role of long-term treatment with lenalidomide and dexamethasone in the development progressive multifocal leukoencephalopathy or intraparenchymal central nervous system myeloma infiltration remains unknown. However, our results suggest that both events may have arisen as a consequence of treatment-related immunosuppression. Thus, an appropriate clinical approach compatible with the simultaneous treatment of progressive multifocal leukoencephalopathy and multiple myeloma should be developed.

Key Points The incidence of mutations within the MAPK pathway, the CRBN pathway, and TP53 is significantly increased in drug-refractory MM. Mutations in CRBN might contribute to IMiD resistance in drug-refractory MM.