ASXL1 and systemic mastocytosis: In a large (879 patients) PMF collaborative study, ASXL1 mutations were identified in 20% of patients and were associated with older age, presence of constitutional symptoms, leukocytosis and circulating blasts.52 In systemic mastocytosis, ASXL1 mutations were seen in 9 (14%) of 62 patients and predicted for a shortened OS.53 In AML, ASXL1 mutations have been found to be mutually exclusive with the favorable NPM1 mutations, with some,54, 55 but not all,56 studies demonstrating an independent prognostic impact.