Dorothy Andersen studied cystic fibrosis in the United States during the early 1900s. In 1935, Andersen discovered lesions in the pancreas of an infant during an autopsy, which led her to classify a condition she named cystic fibrosis of the pancreas. In 1938, Andersen became the first to thoroughly describe symptoms of the medical condition cystic fibrosis. Commonly mistaken for celiac disease prior to the 1900s, Andersen defined cystic fibrosis as the build-up of pancreatic fluid in the body caused by the blockage of pancreatic ducts, and she determined that the two conditions were symptomatically different. Andersen developed an early method for diagnosing cystic fibrosis. By conceptualizing cystic fibrosis and defining its symptoms, Andersen laid the foundation for treatments that enabled infants diagnosed with the disease to survive into adulthood.