Diagnostic and management strategies for Myeloproliferative Neoplasm-Unclassifiable (MPN-U): An international survey of contemporary practice.

Myeloproliferative Neoplasm-Unclassifiable (MPN-U) is defined as an MPN that fails to meet the diagnostic criteria for any of the other defined classical or 'non-classical' MPNs. The reported incidence is variable, dependent on appropriate recognition, and the clinical course can be highly variable ranging from an indolent disorder through to an aggressive disease course with a significant risk of thrombosis, bulky splenomegaly, and debilitating symptom burden. Clinicians frequently manage these conditions according to the clinical concerns e.g. splenomegaly akin to the phenotype, but no evidence base exists. Currently, there are no widely accepted guidelines to deal with both the diagnostic work up and subsequent clinical management of this entity. We hence surveyed major International MPN centres to gain an understanding of common challenges in MPN-U management in 2021 and aid identification of considerable practice variations where harmonisation would be desirable. Such information is vital to support future consensus guidelines in addition to informing further collaborative studies.