Validation of the WHO-defined 20% circulating blasts threshold for diagnosis of leukemic transformation in primary myelofibrosis

This is the authors' abstract. We don't add key points for this paper.

Leukemic transformation is the most dreaded complication in patients with myeloproliferative neoplasms (MPN); overall risk is estimated at 14% for primary myelofibrosis (PMF), 7% for polycythemia vera (PV) and 4% for essential thrombocythemia (ET) 1 . The dismal prognosis of blast phase MPN (MPN-BP) was recently underlined in a large Mayo Clinic study of 248 informative patients and further validated in a separate cohort of 162 cases recruited from multiple Italian institutions 2 . Current treatment approaches for MPN-BP, including allogeneic hematopoietic stem cell transplant (HCT), are largely ineffective in securing long-term survival 2 . On the other hand, HCT has been shown to produce long-term remissions in ~50% of patients with myelofibrosis, if undertaken before blast transformation 3 . At present, diagnosis of MPN-BP employs the World Health Organization (WHO)-defined criteria for acute myeloid leukemia (AML): presence of ≥20% blasts either in the bone marrow (BM) or in the peripheral blood (PB) 4 . In other words, neither scenario requires compartmental concordance. However, it is currently not clear if this 20% WHO threshold for circulating blasts is valid in the context of primary myelofibrosis (PMF), especially in terms of its prognostic equivalency to that of BM blast percentage-defined blast phase PMF (PMF-BP) and its distinction from accelerated phase disease (PMF-AP), operationally defined by the presence of 10–19% circulating blasts 5 .