Multiple endocrine neoplasia describes one of four different genetic syndromes that share the characteristic of either benign or malignant tumors in more than one gland. Such neoplasias may or may not be limited to glands and can also affect other tissues. They are grouped by the primary gene defect, Type I, Type 2a, Type 2b and familial medullary thyroid cancer, which is also a Type 2 defect.
All four conditions are very rare and occur in no more than 1 in every 20,000 people. In addition, almost all cases occur in people with a family history of the condition. Genetic screening is recommended.