This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Haematology, Subject name: Anatomy
Myelofibrosis leading to a dry tap on bone marrow aspiration is seen with which of the following conditions? 
Select and explain. 
A. Burkitts lymphoma, B. Acute erythroblastic leukemia, C. Acute megakaryocytic leukemia, D. Acute undifferentiated leukemia
C: Acute megakaryocytic leukemia
Answer: C: Acute megakaryocytic leukemia 
Explanation: In some acute megakaryocytic leukemias blasts show megakaryocytic differentiation,which is often accompanied by bone marrow fibrosis caused by the release of fibrogenic cytokines. Acute megakaryocytic leukemia is the most common variant of AML associated with Downs syndrome. The release od PDGF is responsible for marrow fibrosis.( ref Robbins 8th/622,9/e p612, Wintrobe12th/1857-8)