TRAP positivity is seen with:

B i.e. Hairy cell leukemiaRef: Robbins Pathology, 9th edition, page 603Explanation:Hairy Cell Leukemia:Rare chronic leukemia that commonly presents with massive splenomegaly, with tumor cells containing hair-like projectionsAlso known as leukemic reticuloendotheliosis*.Clinical:Commonly presents with massive splenomegaly with obliteration of white pulp and involvement of red pulp, pancytopenia (50%), marrow fibrosis, monocytopenia, infections in 1/3.Bone marrow aspiration biopsies unsuccessful ("dry tap'') in 30 - 50% due to marrow fibrosis.Peripheral Smear:Tumor cells are larger than small lymphocytes, modest pale blue a granular cytoplasm with circumferential threadlike extensions seen with phase contrast microscope, round or indented/folded (oval) nuclei, no distinct nucleoli.Bone Marrow:Prominent cell borders ("fried egg appearance") with formalin fixation.Stains:TRAP.B cell markers.CD 11c, CD25, CD103.Annexin A1.