Thymic neuroendocrine carcinomas with combined features ranging from well-differentiated (carcinoid) to small cell carcinoma. A clinicopathologic and immunohistochemical study of 11 cases.

We reviewed 11 cases of primary thymic neuroendocrine carcinomas with combined features ranging from well-differentiated to poorly differentiated neuroendocrine carcinoma. For 3 asymptomatic patients, tumors were discovered during routine examination. Presentation in the other patients was as follows: Cushing syndrome, 2 patients; chest pain, 3 patients; superior vena cava syndrome, 1 patient; and hypercalcemia and hypophosphatemia, 1 patient. No clinical data were available for the 11th patient. All tumors were located in the anterior mediastinum and treated by surgical excision. The lesions were large and well-circumscribed with areas of hemorrhage and necrosis. They were characterized by areas showing a proliferation of monotonous, round tumor cells adopting a prominent organoid pattern admixed with areas showing sheets of atypical cells with hyperchromatic nuclei, frequent mitoses, and extensive areas of hemorrhage and necrosis. Immunohistochemical studies performed in 6 cases showed strong CAM 5.2 low-molecular-weight cytokeratin positivity in all cases, chromogranin and synaptophysin positivity in 4, Leu-7 in 3, and focal positivity for p53 in 2. Follow-up information for 9 cases showed that all patients died of their tumors between 1 and 4 years after diagnosis. The present cases highlight the heterogeneity of neuroendocrine neoplasms and reinforce the notion that these tumors form part of a continuous spectrum of differentiation.