Figure for the reviewAdvances in myelofibrosis: a clinical case approach published in the October edition (2013) of Haematologica. It shows the hypercellular marrow associated with prefibrotic PMF characterized by the presence of increased numbers of hypolobulated megakaryocytes with atypical forms often present in clusters, increased granulopoiesis and decreased erythropoiesis (left). ET bone marrow is less cellular with largely unremarkable erythropoiesis and granulopoiesis (right). Megakaryopoiesis is increased with large hyperlobulated (staghorn-like) megakaryocytes.