The significance of TGFβ-1 in the fibrogenic process of PMF was demonstrated in a TGFβ-1−/− animal model, where overexpression of thrombopoietin (TPO) failed to induce myelofibrosis, in contrast to the severe bone marrow fibrosis developed in control wild-type mice. Here, TGFB1 is linked to myelofibrosis.