Carcinoid tumor of the thymus: a clinicopathologic report of seven cases with a review of the literature.

Carcinoid tumor of the thymus is a rare neoplasm. Formerly confused with thymoma, a tumor of thymic epithelial cells, carcinoid tumor of the thymus has recently been shown to arise from cells of neuroendocrine origin that are normally present in the thymus. About half of the tumors are either functionally active (usually producing Cushing's syndrome) or are found in association with other endocrine tumors, as part of a multiple endocrine neoplasia syndrome. The remainder occur as symptomatic or asymptomatic anterior mediastinal masses, clinically indistinguishable from thymoma. At least 30% of thymic carcinoids are malignant on the basis of local invasion or metastasis or both. A protracted course, with late recurrence of tumor, is not uncommon. Aggressive surgical extirpation, followed by radiotherapy, offers the best hope for cure.