Thymic carcinoma. Five distinctive histological variants.

Five histologically distinct variants of thymic carcinoma are described: mixed small cell undifferentiated squamous cell carcinoma (three cases), basaloid carcinoma (two cases), mucoepidermoid carcinoma (one case), clear cell carcinoma (one case), and sarcomatoid carcinoma (one case). While forming a heterogeneous group, these tumors bear the common features of an anterior mediastinal location and lack of evidence of a primary tumor elsewhere, marking them as primary thymic neoplasms. All except the sarcomatoid variant are morphologically related to similar malignant neoplasms of other organs. These tumors should be recognized as morphological variants of primary thymic carcinoma and demonstrate the ability of thymic epithelium to differentiate toward a variety of different cell types.