Primary neuroendocrine carcinomas of the thymus

Primary neuroendocrine carcinomas of the thymus are rare and comprise a wid e spectrum of lesions ranging from well-differentiated to poorly-differenti ate neoplasms. The classification of such tumors in the thymus is still con troversial. By convention, the better-differentiate examples have been trad itionally designated as thymic carcinoids and thought to represent the medi astinal counterpart of carcinoid tumors in other foregut locations. However , recent studies have shown that such neoplasms, when arising in the thymus , exhibit a much more aggressive behavior than those originating at other l ocations. We therefore consider these lesions to represent fully malignant neoplasms that fall within the spectrum of neuroendocrine carcinomas. The d esignation of well-, moderately-, or poorly-differentiated thymic neuroendo crine carcinoma is therefore favored for these tumors in the present review . Because such tumors may often adopt unusual morphological appearances, it is important to distinguish them from other more common conditions present ing at this location that may exhibit similar histological features. The cl inicopathologic, immunohistochemical, and differential diagnostic features of these tumors in the mediastinum are discussed. Copyright (C) 1999 by W.B . Saunders Company.