BM biopsy histology in ET in overview (×70) and low-power (×210) field. (A) Survey with hematoxylin and eosin-stained section shows an age-matched cellularity but prominent large to giant mature megakaryocytes in random distribution or loose clusters. (B) Chloroacetate esterase reaction demonstrates a normal amount and distribution of neutrophil granulopoiesis (red) and erythropoiesis besides the prominent megakaryocytes. (C) PAS staining reveals a hyperlobulation of megakaryocyte nuclei (almost staghorn-like) and mature cytoplasm without evidence of significant abnormalities. (D) Reticulin stain discloses no increase in fibers but large megakaryocytes. Images were acquired using Zeiss Axioplan 2, 10×/0.50 and 20×/0.50 EC PlanNeofluar.