Primary thymic adenocarcinomas: a clinicopathological and immunohistochemical study of 16 cases with emphasis on the morphological spectrum of differentiation.

Sixteen cases of primary thymic adenocarcinoma are presented. The patients are 9 men and 7 women between the ages of 22 and 68 years (average, 45 years) who presented with non-specific symptoms including cough, chest pain, and dyspnea. Diagnostic imaging revealed the presence of an anterior mediastinal mass, which was surgically removed in all of the patients. Histologically, none of the tumors was encapsulated and showed different growth patterns including mucinous, non-mucinous, and papillary features. The majority of cases showed mixed growth pattern, and the tumor was limited to the mediastinum with only a few cases extending to lymph nodes or pericardium. In two cases, the adenocarcinoma was associated with a thymoma. Immunohistochemical stains were performed, and their positive staining varied depending on the histology of the tumors, showing positive staining in some cases for keratin 7, keratin 20, CEA, CD5, CD117, and CDX-2. PAX8 and TTF-1 were negative in all the tumors. Follow-up information was obtained in 10 patients over a period of 1 to 12 years, indicating that three patients had died within a period of 14 months, one with brain metastasis, while seven patients have remained alive without recurrence. The cases herein described span the spectrum of thymic epithelial tumors and highlight the importance of recognizing this particular type of carcinoma, as it may follow a different outcome and require different treatment options.