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Table 1. Samples to p53 deletions p 53 deletion FISH aCGH FISH and aCGH MGUS 142 - - SMM 108 - - Newly diagnosed MM - 182 - Relapsed/refractory MM 62 156 19 HMCLs - 48 - Total 312 386 19 Background: Inactivation of p53 by mutation or allelic loss is a rare event in multiple myeloma (MM) at the time of disease diagnosis and believed to be more common in the late stages of the disease. Here we defined the prevalence of p53 deletions in monoclonal gammopathy of undetermined significance (MGUS), smoldering multiple myeloma (SMM), newly diagnosed MM, relapsed MM and human myeloma cell lines (HMCLs). Indirect mechanisms of p53 inactivation such as amplification of MDM2, or deletion of CDKN2A (p14ARF) were also investigated. Patients and Methods: A total of 631 MM samples and 48 HMCLs were analyzed for p53 abnormalities (Table 1) and compared with a cohort of plasma cell leukemia (PCL) previously published by us. Interphase fluorescence in situ hybridization (FISH) and highresolution array-based comparative genomic hybridization (aCGH) were used to detect p53 deletions. MDM2 amplification and p14ARF loss were evaluated by aCGH. Overall survival (OS) was estimated through Kaplan Meier method. Results: The prevalence of p53 deletions was 1.4%, 3.7%, 8.9%, 20% and 87.5% in MGUS, SMM, newly diagnosed MM, relapsed MM and HMCLs respectively (Figure 1). Of interest patients in first relapse showed a p53 deletion prevalence of 18% in comparison with 33% for patients in second relapse or more. We obtained p53 deletion status in 8 patients noted to have deletion at the time of relapse and in whom we had previous samples stored. In 7 of 8 cases deletions had been acquired (absent in the previous samples). The median OS for relapsed MM patients with or without p53 deletion were 4.2 months and 37.8 months respectively (p <0.001). MDM 2 amplification and p14ARF loss was detected in 0.4% and 2% of new diagnosed MM, 0.6% and 5.1% of relapsed MM and 2% and 29% of HMCLs respectively. Discussion: Emergence of p53 deletion/mutations denotes progression genetic events in MM. Importantly we show for the first time the overriding importance of p53 deletions as prognostic markers in relapsed MM. A molecular staging system that is based on the presence of p53 inactivation may be more powerful than classifying patients based on the loss of p53. Other abnormalities involving p53 pathway regulators like MDM2 gain and p14ARF loss are infrequent events in MM, even in advanced disease. Figure 1. Prevalence of p53 deletions Figure 1. Prevalence of p53 deletions

616 Background: We have shown the three drug combination of cyclophosphamide, bortezomib and dexamethasone (CyBorD) to be highly active therapy in newly diagnosed myeloma while allowing stem cell harvest and transplantation (Reeder et al. Leukemia 2009; 23:1337-1341). However, twice weekly bortezomib and high dose dexamethasone have been shown to cause significant toxicities. In a prospective Phase II we modified CyBorD by using bortezomib once weekly and reducing the dexamethasone to “low dose dex” after the first two cycles in an attempt to reduce toxicity (cohort 2). We report the efficacy and toxicity of this modified regimen and compare the results to standard CyBorD (cohort 1). Patients and methods: 63 untreated symptomatic patients were enrolled on this Phase II trial (33 on cohort 1 and 30 on cohort 2). All are evaluable for response and toxicity. Treatment on cohort 2 consisted of oral cyclophosphamide 300 mg/m2 and IV bortezomib 1.5 mg/m2 days 1, 8, 15 and 22 and dexamethasone 40 mg by mouth days 1-4, 9-12, 17-20 in cycles 1 and 2, then 40 mg po days 1, 8, 15, 22 in cycles 3 and beyond. Cohort 1 used standard dosing of bortezomib and high dose dexamethasone throughout. Each cycle was 28 days. Acyclovir and a quinolone antibiotic prophylaxis were routinely used. Patients were evaluated for response and toxicity every cycle and were offered stem cell harvest and transplant after the 4th cycle but could continue up to 12 cycles maximum. Results: The median age for all 63 patients was 61 (36-74) years and 48% were female. Durie-Salmon stages were 47% II and 50% III and ISS stages I 43%, II 36%, and III 21%. Twenty-four percent of patients were genetic high risk (t(4;14) or deletion 17). Cohorts I and II were matched for age, gender and ECOG PS. ISS stages were higher in cohort 1 than cohort 2 (II/III 67% vs. 44%). The intent to treat (ITT) ORR (≥PR) for all 63 patients (cohorts 1 and 2) is 90% with 60% ≥VGPR. For cohort 2 (modified CyBorD) the ITT overall response (≥PR) was 93% (CR: 5, nCR: 7, VGPR: 6, PR: 10) with 60% ≥VGPR and 40% ≥ nCR. Those completing all 4 cycles of therapy had 92% ORR (24/26) and 65% (17/26) ≥VGPR. A comparison of response rates in cohorts 1 and 2 is shown in table 1. These high and comparable response rates were associated with fewer grade 3+ adverse events (AE's) than in cohort 1 (37% vs. 48%) and no grade 3 peripheral neuropathy (PN). The median follow-up for all 63 patients is 12.4 (2.8-29.2) months and 95% of patients are alive with 87% free from progression. Conclusions: Modified CyBorD with weekly bortezomib and reduced dexamethasone retains the high activity seen in standard CyBorD, but is less toxic and more convenient. Interestingly, this modified regimen allowed higher overall doses of bortezomib (5.2 vs. 6.0 mg/m2 per cycle) yet overall neuropathy rates were similar. This combination of a weekly alkylating agent with bortezomib and dexamethasone is well tolerated and produces high response rates in newly diagnosed patients with multiple myeloma. Disclosures: Reeder: Millennium (MPI): Research Funding; Celgene: Research Funding. Reece:Ortho Biotech: Honoraria, Research Funding. Chen:Celgene: Honoraria, Research Funding; Ortho Biotech: Honoraria. Hentz:Millennium (MPI): Research Funding. Fonseca:Otsuka: Consultancy; BMS: Consultancy; Amgen: Consultancy; Medtronic: Consultancy; Genzyme: Consultancy. Bergsagel:Merck: Research Funding; Amgen: Consultancy; Genentech: Consultancy; Celgene: Consultancy. Stewart:Proteolix: Honoraria; Millennium (MPI): Research Funding.