Acute promyelocytic leukemia (APL) is a distinct type of acute myeloid leukemia that is defined by the presence of the translocations that mostly involve the RARA gene. The most frequent translocation is the t(15;17), which fuses the RARA gene with the PML gene. Previous studies have shown that other cooperative mutations are required for the development of APL after the initiating event of the t(15;17). In this study, we combined cytogenetics with next-generation sequencing and single-nucleotide polymorphism array to study the genetic complexity in 20 APL cases diagnosed in our institution. All but 3 cases had additional genetic aberrations. Our study demonstrated that somatic mutations are frequent events in APL. In addition to the previously reported recurrent cooperative mutations in the FLT3, WT1, and RAS genes, we identified mutations in several epigenetic modifiers, including TET2, EZH2, and DNMT3A, co-occurring with either FLT3 or WT1 mutations. Mutations of the WT1 gene and chromosome 11p copy neutral loss of heterozygosity affecting WT1 are present in a third of the cases in our series. Two-thirds of APL cases in our study demonstrated a global reduction but focal accumulation of H3K27 methylase (H3K27me) expression, indicating a disorganized chromatin methylation pattern with generally more accessible chromatin status. Our study confirmed genetic complexity of APL and revealed that epigenetic aberrations are more common than previously expected. Although epigenetic modulation is not a common treatment strategy in APL, targeting this pathway may have some clinical utility in refractory or relapsed APL cases.
Keywords: Acute promyelocytic leukemia; Copy neutral loss of heterozygosity; Epigenetics; Next-generation sequencing; SNP array; Somatic mutations.
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