Abstract Myelofibrosis (MF) is a clonal malignancy frequently characterized by anemia and in 10%–20% of cases it can evolve into blast phase (BP). Anemia in MF is associated with reduced survival and ‐in primary MF‐ also with an increased probability of BP. Conventional treatments for anemia have limited effectiveness in MF. Within a dataset of 1752 MF subjects largely unexposed to ruxolitinib (RUX), BP incidence was 2.5% patients per year (p‐y). This rate reached respectively 4.3% and 4.5% p‐y in case of patients with common terminology criteria for adverse events (CTCAE) grade 3/4 and grade 2 anemia, respectively, that represented together 32% of the cohort. Among 273 MF cases treated with RUX, BP incidence was 2.89% p‐y and it reached 4.86% p‐y in subjects who started RUX with CTCAE grade 2 anemia (one third of total). Within patients with red blood cell transfusion‐dependency at 6 months of RUX (21% of the exposed), BP rate was 4.2% p‐y. Our study highlights a relevant incidence of BP in anemic MF patients, with a similar rate whether treated with or without RUX. These findings will help treating physicians to make decisions on the safety profile of innovative anemia treatments.
