Highly variable mutational profile of ASXL1 in myelofibrosis

Prognostic value of ASXL1 mutations in patients with primary myelofibrosis and its relationship with clinical features: a meta-analysis

Additional sex combs like 1 (ASXL1) mutations are one of the most common molecular biological abnormalities in patients with primary myelofibrosis (PMF), and the effect of these mutations on prognosis remains controversial. Hence, we conducted a meta-analysis to assess the prognostic value and clinical characteristics of ASXL1 mutations in PMF patients. Eligible studies were systematically searched from PubMed, Embase, and the Cochrane Library. We extracted the hazard ratios (HRs) and their 95% confidence intervals (CIs) of overall survival (OS) and leukemia-free survival (LFS), the number of patients transformed to acute leukemia, and clinical characteristics to carry out a meta-analysis by fixed effect model or random effect model according to the heterogeneity between studies. A total of 4501 PMF patients from 16 cohorts of 14 studies were included in this meta-analysis. The results revealed that ASXL1 mutations might predict a shorter OS (HR = 2.30, 95% CI: 1.79-2.94, P < 0.00001) and a higher probability of transformation to acute leukemia (LFS: HR = 1.77, 95% CI: 1.30-2.42, P = 0.0003; the rate of acute leukemia transformation: OR = 2.06, 95% CI: 1.50-2.83, P < 0.00001). Furthermore, ASXL1 mutations were correlated with patients older than 65 years old, male, a lower level of platelet counts, and a higher risk of the international prognostic score system. These findings indicate that ASXL1 mutations have a significant adverse impact on the prognosis of PMF patients and may contribute to risk stratification and prognostic assessment for PMF patients.

ASXL1/EZH2 mutations promote clonal expansion of neoplastic HSC and impair erythropoiesis in PMF

Primary myelofibrosis (PMF) is a hematopoietic stem cell (HSC) disease, characterized by aberrant differentiation of all myeloid lineages and profound disruption of the bone marrow niche. PMF samples carry several mutations, but their cell origin and hierarchy in regulating the different waves of clonal and aberrant myeloproliferation from the prime HSC compartment is poorly understood. Genotyping of >2000 colonies from CD133+HSC and progenitors from PMF patients confirmed the complex genetic heterogeneity within the neoplastic population. Notably, mutations in chromatin regulators ASXL1 and/or EZH2 were identified as the first genetic lesions, preceding both JAK2-V617F and CALR mutations, and are thus drivers of clonal myelopoiesis in a PMF subset. HSC from PMF patients with double ASXL1/EZH2 mutations exhibited significantly higher engraftment in immunodeficient mice than those from patients without histone modifier mutations. EZH2 mutations correlate with aberrant erythropoiesis in PMF patients, exemplified by impaired maturation and cell cycle arrest of erythroid progenitors. These data underscore the importance of post-transcriptional modifiers of histones in neoplastic stem cells, whose clonal growth sustains aberrant myelopoiesis and expansion of pre-leukemic clones in PMF.