Pulmonary embolism (PE) is a blockage of the lung's main artery or one of its branches by a substance that has traveled from elsewhere in the body through the bloodstream (embolism). PE results from a deep vein thrombosis (commonly a blood clot in a leg) that breaks off and migrates to the lung, a process termed venous thromboembolism (VTE). A small proportion of cases are caused by the embolization of air, fat, or talc in drugs of intravenous drug abusers or amniotic fluid. The risk of PE is increased in various situations, such as cancer or prolonged bed rest.