A rare, fast-growing cancer that forms in the tissues of the lung and pleura (the thin layer of tissue that covers the lungs and lines the inside of the chest). It may also form in the organs between the lungs, including the heart, aorta, and pulmonary artery, or in the diaphragm. Pleuropulmonary blastoma may sometimes spread to other parts of the body, especially to the brain. It usually occurs in infants and young children. Some patients with pleuropulmonary blastoma have mutations (changes) in a gene called DICER1.