9Swedish Acute Myeloid Leukemia Group, SwedenOur knowledge about acute promyelocytic leukemia (APL) patients is mainly based on data from clinical trials, whereas population-based information is scarce. We studied APL patients diagnosed between 1997 and 2006 in the populationbased Swedish Adult Acute Leukemia Registry. Of a total of 3897 acute leukemia cases, 3205 (82%) had non-APL acute myeloid leukemia (AML) and 105 (2.7%) had APL. The incidence of APL was 0.145 per 100 000 inhabitants per year. The median age at the time of diagnosis was 54 years; 62% were female and 38% male. Among younger APL patients, female sex predominated (89% of patients o40 years). Of the 105 APL patients, 30 (29%) died within 30 days (that is, early death (ED)) (median 4 days) and 28 (26%) within 14 days from diagnosis. In all, 41% of the EDs were due to hemorrhage; 35% of ED patients never received all-trans-retinoic acid treatment. ED rates increased with age but more clearly with poor performance status. ED was also associated with high white blood cells, lactate dehydrogenase, creatinine, C-reactive protein and low platelet count. Of non-ED patients, 97% achieved complete remission of which 16% subsequently relapsed. In total, 62% are still alive at 6.4 years median follow-up. We conclude that ED rates remain very high in an unselected APL population.

The extent and role of aberrant DNA methylation in promoter CpG islands (CGIs) have been extensively studied in leukemia and other malignancies. Still, CGIs represent only a small fraction of the methylome. We aimed to characterize genome-wide differential methylation of cytogenetically normal AML (CN-AML) cells compared with normal CD34(+) bone marrow cells using the Illumina 450K methylation array. Differential methylation in CN-AML was most prominent in genomic areas far from CGIs, in so called open sea regions. Furthermore, differential methylation was specifically found in genes encoding transcription factors (TFs), with WT1 being the most differentially methylated TF. Among genetic mutations in AML, DNMT3A mutations showed the most prominent association with the DNA methylation pattern, characterized by hypomethylation of CGIs (as compared with DNMT3A wild type cases). The differential methylation in DNMT3A mutant cells vs. wild type cells was predominantly found in HOX genes, which were hypomethylated. These results were confirmed and validated in an independent CN-AML cohort. In conclusion, we show that, in CN-AML, the most pronounced changes in DNA methylation occur in non-CGI regions and that DNMT3A mutations confer a pattern of global hypomethylation that specifically targets HOX genes.

This study was designed to analyze the effect of global and gene-specific DNA methylation patterns on the outcome of patients with acute myeloid leukemia (AML). Methylation of CDKN2B (p15), E-cadherin (CDH) and hypermethylated in cancer 1 (HIC1) promoters and global DNA methylation by luminometric methylation assay (LUMA) was analyzed in 107 AML patients and cytogenetic and molecular mutational analysis was performed. In addition, genome-wide promoterassociated methylation was assessed using the Illumina HumanMethylation27 array in a proportion of the patients. Promoter methylation was discovered in 66, 66 and 51% of the patients for p15, CDH and HIC1, respectively. In multivariate analysis, low global DNA methylation was associated with higher complete remission rate (hazard ratio (HR) 5.9, P ¼ 0.005) and p15 methylation was associated with better overall (HR 0.4, P ¼ 0.001) and disease-free survival (HR 0.4, P ¼ 0.016). CDH and HIC1 methylation were not associated with clinical outcome. Mutational status and karyotype were not significantly associated with gene-specific methylation or global methylation. Increased genome-wide promoter-associated methylation was associated with better overall and disease-free survival as well as with LUMA hypomethylation. We conclude that global and gene-specific methylation patterns are independently associated with the clinical outcome in AML patients.