What are MPNs?MPNs are diseases that affect how blood cells are produced in our bodies. Our bodies normally produce billions of blood cells every day. This process occurs inside our bones, in the bone marrow. The bone marrow contains stem cells which grow and mature into all the blood cells that our bodies need: Red blood cells, white blood cells and platelets. Each one of these types of cells has a specific job to do inside our bodies. When a person is diagnosed with myeloproliferative neoplasm (MPN) something has gone wrong with their blood cell production. The bone marrow begins to produce either too many blood cells, or sometimes too few. There are three common types of MPNs, but there are other types as well. MPNs are classed by the World Health Organization as a blood cancers because the bone marrow is producing blood cells in an uncontrolled way. The three common types of MPNs are separated into different disorders as each of them affect blood cell levels in a different way. These three most frequently diagnosed types are: Essential thromobythaemia (ET) Polycythaemia vera (PV) Myelofibrosis (MF) Click on the links above to learn more about the individual MPNs.