A risk factor [2] is anything that increases a person’s chance of developing a tumor. Although risk factors often influence the development of a tumor, most do not directly cause a tumor. Some people with several risk factors never develop a tumor, while others with no known risk factors do.

The cause of PPB is not known. Most often it develops randomly. For most children with PPB, there may have been no personal or family history of the disease before the PPB occurred; in other words, there was no reason to suspect that the child would develop PPB. Most family members of children with PPB are healthy. The following factors may raise a person’s risk of developing PPB.

Pre-existing cysts. Children with air-filled lung cysts may have a higher risk of developing PPB, but most children with lung cysts do not have PPB.

Family history. About 40% of children with PPB have a family history of lung cysts, kidney cysts (called cystic nephroma, which is very rare), Wilms tumor [3], thyroid [4] lumps (sometimes cancerous), rare ovarian tumors (called Sertoli-Leydig cell tumors), leukemia, rhabdomyosarcoma [5], peripheral primitive neuroectodermal tumor [6], and small bowel polyps (also called hamartomatous polyps, which are noncancerous masses of normal tissue on the small intestine). These situations are rare, and very few doctors have experience with them. Also, a mutation in a gene called DICER1 has been found in families with PPB.