This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Blood, Subject name: Pathology
[{'content': 'TRAP positivity is seen with: \nSelect and explain. \nA. CML, B. Hairy cell leukemia, C. CLL, D. Follicular lymphoma', 'role': 'user'}, {'content': 'Answer: B \nExplanation: 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.', 'role': 'assistant'}]