TGFB1 and myelofibrosis: Given that in myelofibrosis the immature megakaryocytes contain high levels of the pro-fibrotic growth factor TGF-β [10,11,12,13], these cells are thought to induce fibrosis by releasing TGF-β, which stimulates the cells of the bone marrow microenvironment to secrete and polymerize collagen [14,15].