A,B: Bone marrow biopsy from 50-year old female with post-PV MF prior to allo-SCT. The marrow is markedly hypercellular for age (100% cellularity) and contains large clusters of abnormal megakaryocytes with hyperchromatic and “cloud-like” nuclei, as well as smaller forms with hyperlobulated nuclei. Reticulin stain shows grade 2 of 3 fibrosis (A, hematoxylin & eosin; B, reticulin stain). C,D: Bone marrow biopsy taken 12 months after allo-SCT shows cellularity with normal range for the patient’s age (60% celluarity), with a normal myeloid:erythroid ratio and morphologically normal megakaryocytes that do not cluster. Reticulin stain shows resolution of reticulin fibrosis (grade 0). Chimerism studies on bone marrow showed >98% donor origin (C, hematoxylin & eosin; D, reticulin stain).