ALBERT

Description: Abstract 4280 The prognosis for patients with AML who fail front line cytarabine/anthracycline-based chemotherapy is poor. Fewer than 10% of patients are expected to respond to second line chemotherapy and survival averages a few months. Decitabine is currently being used as a front line agent for patients with AML who are unfit for intensive chemotherapy generally because of advanced age. However in published studies the complete response rate in this population is only 25% (Cashen et al, JCO 2010). We recently treated 9 patients with primary refractory AML who failed cytarabine/anthracycline based chemotherapy with decitabine 20 mg/m2 × 5 days every 4–5 weeks. The median age was 59 years (range 40–83). There were 5 men and 4 women. Prior AHDs and comorbid conditions included MDS in 2 patients (both were treated with azacytidine), HIV in one patient, polycythemia vera in one patient, and breast ca treated with chemotherapy and radiation in one patient. Cytogenetics were normal in 2 patients, other intermediate in 3 patients and poor risk in 4 patients. Initial therapy of AML was cytarabine 3 gm/m2 × 5 and mitoxantrone 80 mg/m2 × 1 in 4 patients, 3+7 in 4 patients, and CPX-351 in 1 patient. 2 patients additionally had 2 courses of gemtuzumab ozogamicin with no response after front line chemotherapy and before decitabine. The median initial blast percentage prior to decitabine was 22% (range 7–73%), and after decitabine 5% (range 1–44%). 5 patients (56%) had a CR, 2 patients (22%) had a PR and 2 patients (22%) had progressive disease, including one who was extensively pretreated with azacytidine for prior MDS. The median number of decitabine cycles was 6 (range 1–12). Median time to progression was 11 months (range 1–20 months, with 2 patients remaining in CR at 10 and 14 months). 3 patients underwent allogeneic stem cell transplant after response to decitabine. One remains in CR 10 months post initiation of decitabine, and 6 months post bmt done in PR. One patient died of complications of GVHD 20 months post initiation of decitabine and 12 months post BMT, and one patient died of relapsed disease 18 months post initiation of decitabine and 10 months post BMT. The median survival is 12 months (range 10–20 months). We saw a high response rate to decitabine in patients with primary refractory AML. Although this could have occurred by chance due to the small sample size, we propose that decitabine might be more effective in patients who have undergone cytoreduction with intensive chemotherapy than in patients who have not received such therapy. Alternatively, lack of response to cytarabine/anthracycline therapy could select out a group of patients more likely to respond to decitabine. Disclosures: Off Label Use: Use of decitabine in AML. Seiter:Eisai: Speakers Bureau.

Description: Introduction: Genomic studies of chronic lymphocytic leukemia (CLL) have uncovered 〉80 potential driver mutations. The vast majority of these mutations affect coding regions, and just two potential drivers have been identified in non-coding elements. Aim: To describe the biological and clinical impact of a recurrent A〉C mutation at the third base of the small nuclear RNA U1, the non-coding component of the spliceosome involved in the recognition of the 5' splice site (5'SS). Methods: Whole-genome sequencing (WGS) and RNA-seq from 318 CLL patients were used to identify and characterize a highly recurrent A〉C point mutation occurring at position 3 of the U1 snRNA gene (g.3A〉C mutation). The U1 wild-type and mutant forms were introduced into three CLL cell lines (JVM3, HG3, MEC1) to validate in vitro the predicted effect of this alteration. We screened two independent cohorts including a total of 1,314 CLL patients for the presence of the mutation using the rhAmp SNP genotyping assay, and integrated the U1 mutational status with well-known driver alterations, IGHV and epigenetic subgroups, and clinical parameters. Results: The U1 mutation was found in 8/78 (10.3%) CLL cases analyzed by WGS. Given its role in 5'SS recognition by base-pairing, we reasoned that this mutation was likely to alter the splicing and expression patterns of CLL. We were able to confirm widespread specific alterations in the transcriptome by comparing RNA-seq data between wild-type and g.3A〉C mutated samples. Applying this knowledge to an algorithm aimed to infer the U1 mutational status from expression data, we were able to identify 4 mutated cases among 240 additional cases that had RNA-seq but no WGS. In total, 12/318 (3.8%) CLL patients analyzed by WGS and/or RNA-seq harbored this mutation. This g.3A〉C U1 mutation changes the preferential A-U base-pairing between U1 and 5'SS to C-G base-pairing, creating novel splice junctions and altering the splicing pattern of 3,193 introns in 1,519 genes. In addition to altered splicing, 869 genes were differentially expressed between mutated and wild-type cases. We identified specific cancer genes (e.g. MSI2, POLD1, or CD44) and pathways (B-cell receptor signaling, promotion of apoptosis, telomere maintenance, among others) altered by the U1 mutation. To confirm a causal link between this mutation and splicing changes, we introduced exogenous U1 genes with or without the mutation into three cell lines. Subsequent RNA-seq of these cell lines recapitulated the altered splicing and expression patterns observed in CLL patients. We next screened for the presence of the U1 mutation 1,057 patients (cohort 1) using the rhAmp assay and it was found in 30 (2.8%) cases. The distribution of the mutation was similar in Binet stages and CLL vs monoclonal B-cell lymphocytosis. However, the U1 mutation was almost always found in IGHV unmutated CLL (29/30, p=9.0e-11) and within the naïve-like CLL epigenetic subgroup (p=3.7e-7). None of the U1 mutated cases had mutations in the SF3B1 splicing factor. Considering only pre-treatment CLL samples, U1 mutation was associated with a shorter time to first treatment independently of the Binet stage, IGHV mutational status, epigenetic subgroups, and mutations in the well-known CLL drivers SF3B1, NOTCH1, ATMor TP53. In cohort 2 (n=257), this mutation was found in 13 (5.1%) patients, confirming its enrichment in IGHV unmutated cases, naïve-like epigenetic subgroup, and splicing modulation. Despite the relatively small number of pre-treatment samples carrying the U1 mutation (7/178) and short follow-up of the patients (median 2.6 years), the effect of this mutation on time to first treatment in cohort 2 was compatible with the one observed in cohort 1. Finally, we screened for the U1 mutation a cohort of diffuse large B-cell lymphoma (n=108), mantle cell lymphoma (n=101), follicular lymphoma (n=87), splenic marginal zone lymphoma (n=12), acute myeloid leukemia (n=52), and myelodysplastic syndrome (n=67). The mutation was not present in any of the samples analyzed. Conclusions: Here we have reported that the third base of the small nuclear RNA U1 is recurrently mutated in CLL, proved its effect in splicing and gene expression, and shown that this mutation is independently associated with faster disease progression. The g.3A〉C U1 mutation represents a novel non-coding driver alteration in CLL with potential clinical and therapeutic implications. Disclosures Ramirez Payer: GILEAD SCIENCES: Research Funding. Terol:Astra Zeneca: Consultancy; Gilead: Research Funding; Abbvie: Consultancy; Janssen: Consultancy, Research Funding; Roche: Consultancy. Lopez-Guillermo:Celgene: Consultancy, Research Funding; Janssen: Research Funding; Roche: Consultancy, Research Funding; Gilead: Consultancy, Research Funding.