PF4 and acute myeloid leukemia: Although the exact mechanism of myelofibrotic progression in AML is unclear, one study suggested that certain factors are released by proliferating megakaryocytes because they are unable to store these factors (platelet-derived growth factor, fibroblast growth factor, platelet factor-4, transforming growth factor-β and beta-thromboglobulin) in defective α particles, which promote the growth of bone marrow fibroblasts (29).