Clinicopathological characterisation of myeloproliferative neoplasm‐unclassifiable (MPN‐U): a retrospective analysis from a large UK tertiary referral centre

Summary Myeloproliferative neoplasm‐unclassifiable (MPN‐U) presents an MPN‐type phenotype that fails to meet diagnostic criteria for other MPN variants. Variability in the clinicopathological phenotypes presents many challenges. Amongst a registry cohort of 1512 patients with MPN, 82 with MPN‐U were included, with a median (range) age of 49·7 (13–79) years. Albeit heterogeneous, common presentation features included raised lactate dehydrogenase, thrombocytosis and clustered/pleomorphic megakaryocytes on trephine biopsy. Thrombosis was common (21%), necessitating vigilance. The median event‐free survival was 11·25 years (95% confidence interval 9·3–not reached), significantly shortened in cases with lower platelet counts (<500 × 109/l) and a leucocytosis (≥12 × 109/l) at presentation. Generation of potential MPN‐U prognostic scores is required.