Thymic carcinoma: current concepts and histologic features.

Thymic carcinoma is a rare tumor that has traditionally posed a significant challenge for diagnosis to clinicians and histopathologists. No reliable histopathologic features have yet been identified that can permit reliable distinction of these tumors from a metastasis to the mediastinum. Histologically, the tumors are characterized by morphologic features that are indistinguishable from those arising from a variety of other epithelial organs. A large number of histologic variants have been described. In general, these tumors remain a diagnosis of exclusion and, as a group, represent high-grade neoplasms with a very aggressive clinical behavior and an often-ominous prognosis.