MPL and essential thrombocythemia: Various somatic mutations, such as MPL-W515L, W515K, W515A, W515R, and W515-P518delinsKT, have also been detected in MPN samples, such as polycythaemia vera (PV), primary myelofibrosis (PMF) and essential thrombocythaemia (ET), which manifest as the overproduction of one or more myeloid lineages.