Primary neuroendocrine carcinoma of thymus: a rare cause of Cushing's syndrome.

Thymomas constitute majority of the thymic neoplasms. In contrast, neuroendocrine tumors (carcinoid and neuroendocrine carcinoma) of thymus are extremely rare. Thymic carcinoids may present rarely with Cushing's syndrome due to the ectopic production of adrenocorticotropic hormone (ACTH). Recognition of this association is imperative for appropriate management of patients. We describe three cases of rare atypical carcinoid tumor (neuroendocrine carcinoma) of the thymus. Case 1, of a 26-year-old man presenting with Cushing's syndrome, case 2--a 23-year-old female with Cushingoid features, and Case 3--a 39-year-old man complaining of progressively worsening dyspnea. Computed tomography (CT) scans of chest in all three patients revealed anterior mediastinal mass. Excision of tumors and histological examination of the three tumors showed a carcinoid tumor with nuclear pleomorphism, increased mitotic activity and focal necrosis. The features suggested a diagnosis of atypical carcinoid tumor in all the three cases. The tumor cells in Cases 1 and 2 showed focal immunohistochemical staining for ACTH. Atypical carcinoid (neuroendocrine carcinoma, well-differentiated and moderately-differentiated) of the thymus is a rare thymic tumor which carries a worse prognosis compared to thymoma and requires aggressive therapy. Hence, an accurate diagnosis is essential.