Rare Disorder

A non-neoplastic or neoplastic disorder with an extremely low prevalence. Because of its infrequency, it may be subject to delayed diagnosis and often a lack of definitive treatment. As of May 2026, the prevalence that allows a condition to be classified as a rare disorder is less than 200,000 cases in the US and less than 5 cases per 10,000 people in Europe.

Source: NCI Thesaurus (C4873).