Myeloproliferative Neoplasms are chronic diseases; they encompass Polycythemia Vera, Essential Thrombocythemia, and Primary Myelofibrosis with shared mutations that constitutively activate the physiologic signal-transduction pathways responsible for hematopoiesis. Myelofibroses may arise either as primary or antecedent to Polycythemia Vera and Essential Thrombocythemia. Myelofibrosis is the least common and the most aggressive of these diseases leading to death in 5 to 7 years due to bone marrow failure, massive splenomegaly related to extra medullary hematopoiesis, constitutional symptoms and cachexia.