Morphologic change after IFN therapy in a patient with primary myelofibrosis. (A-D) Before treatment (2002). (A) The area of myelofibrosis (left), with preserved residual foci of hematopoiesis, and abnormal megakaryocyte morphology (right). (B) Abnormal megakaryocyte morphology. (C) 2+ reticulin fibrosis. (D) Collagen fibrosis. (E-H) After treatment (2009). (E) Improved bone marrow architecture, hematopoiesis, and megakaryocyte morphology. (F) Improved megakaryocyte morphology and increased normoblastic erythropoiesis. (G) Minimal reticulin fibrosis. (H) Absent collagen fibrosis.