Questions about MPNs The chances are you had never heard of myeloproliferative neoplasms (MPNs) until you or someone in your family was diagnosed. Myeloproliferative neoplasms, also called myeloproliferative disorders, are a spectrum of blood cancers*, ranging from mild to more aggressive conditions. There are three main types of MPNs called essential thrombocythaemia (ET), polycythaemia vera (PV) and myelofibrosis (MF). MPNs are rare and they can strike people of any age, even children. The three MPNs are distinct diseases but they have one feature in common –– they affect the levels of blood cells produced in our bodies. *MPNs are classed by the World Health Organization as a blood cancers because blood cells are produced in an uncontrolled way.