BM biopsy histology in ET/PV in low-power (×170) or medium-power (×350) field. (A) Survey with hematoxylin and eosin-stained section shows hypercellularity with conspicuous small to giant megakaryocytes and increased erythropoiesis and granulopoiesis. (B) Chloroacetate esterase reaction indicates panmyelosis or a PV-like picture: proliferation of neutrophil granulopoiesis (red) and large inlets of nucleated erythroid precursors intermingled with small to large megakaryocytes. (C) PAS staining demonstrates large to giant megakaryocytes, some with hyperlobulated (staghorn-like) nuclei surrounded by mature cytoplasms (resembling ET; see Figure 1C). (D) PAS staining with grouping of small to giant megakaryocytes with moderate nuclear lobulation consistent with a PV-like appearance. Images were acquired using Zeiss Axioplan 2, 20×/0.50 and 40×/0.60 EC PlanNeofluar.