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Thymic neuroendocrine (carcinoid) tumors

Jonathan R Strosberg, MD
Mark F Berry, MD
Henry D Tazelaar, MD
Section Editors
James R Jett, MD
Sally E Carty, MD, FACS
Joseph S Friedberg, MD
Deputy Editor
Diane MF Savarese, MD


Thymic neuroendocrine tumors (NETs), otherwise known as thymic carcinoid tumors, are uncommon primary thymic neoplasms with neuroendocrine differentiation that generally present as a mass within the anterior mediastinum. This topic review will cover the epidemiology, pathology, classification, clinical presentation, staging, and treatment of NETs arising in the thymus. Thymomas and thymic carcinomas are addressed separately, as are the diagnostic evaluation of patients with a mediastinal mass and the differential diagnosis of an anterior mediastinal mass. (See "Clinical presentation and management of thymoma and thymic carcinoma" and "Approach to the adult patient with a mediastinal mass".)


The thymus is an anterior mediastinal organ that weighs 12 to 15 grams at birth, reaches its maximum weight of 40 grams around puberty, and then involutes and persists in an atrophic state into old age. The gland is composed of a central medulla and an outer cortex, surrounded by an outer capsule. The thymus consists primarily of epithelial cells, keratinized epithelial cells (Hassall's corpuscles), myoid cells, thymic lymphocytes ("thymocytes"), and B-lymphocytes, which may rarely form germinal centers. The thymus is primarily involved in the processing and maturation of lymphocytes, which become T-lymphocytes upon release into the circulation. (See "Normal B and T lymphocyte development", section on 'T cell development'.)


Thymic malignancies as a group are relatively rare (0.2 to 1.5 percent of all malignancies, 0.13 cases per 100,000 population in the United States), but they are among the most common mediastinal primary tumors [1,2].

Of the primary thymic malignancies, neuroendocrine tumors (NETs) are the least common, accounting for 2 to 5 percent of thymic tumors [3,4]. A thymic primary site accounts for approximately 0.4 percent of all carcinoid tumors; this corresponds to an estimated annual incidence in the United States of approximately 0.2 per million [5,6]. (See "Pathology of mediastinal tumors".)

Almost all cases have been reported in adults, with a median age of approximately 54 years and a strong male preponderance [4,5,7-11]. The largest reported series of thymic NETs consists of 160 patients who were reported to the Surveillance, Epidemiology, and End Results (SEER) database over a 33-year period [5]. The median age at presentation was 57, and the male to female ratio was 3:1. Disease was confined to the thymus, locally invasive (or involving regional lymph nodes), or distantly metastatic in 27, 36, and 28 percent of cases, respectively. Histologically, tumors were classified as well-differentiated, moderately-differentiated, or poorly-differentiated/anaplastic in 58, 10, and 12 percent of cases, respectively.

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Literature review current through: Oct 2017. | This topic last updated: Mar 27, 2017.
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