The ‘classical’ Philadelphia chromosome-negative myeloproliferative neoplasms (MPN), essential thrombocythaemia (ET), primary myelofibrosis (PMF) and polycythaemia vera (PV), are characterized by clonal myeloproliferation with effective maturation causing accumulation of terminally differentiated cells in the peripheral blood and/or splenomegaly. Although each disease has distinct clinical manifestations clonal haematopoiesis is driven, in most cases, by upregulation of the Janus kinase (JAK)–signal transducer and activator of transcription (STAT) pathway [1]. Polycythaemia vera and ET are relatively indolent, with most patients having nearly normal life expectancy, in contrast to PMF [2]. Thrombosis and haemorrhage are the main causes of morbidity and mortality in both PV and ET, and evolution to myelofibrosis (MF) and/or accelerated/blast phase (AP/BP) is estimated to occur in 10% of patients [3, 4]. Overt (classical) PMF is the most aggressive of the three diseases, with a median overall survival of five years. The most common causes of mortality are transformation to BP (20 to 25% of patients), thrombosis, cardiovascular complications and infections [5]. However, it is important to note that incidence figures, survival and also risk-factor determinations may be inaccurate and at times conflicting because of the inadvertent labelling in some studies of patients with prefibrotic/early PMF (prePMF) or ‘masked’(prodromal) PV as ET [6–8].