Sebaceous lymphadenoma of the thymus: A clinicopathologic and immunohistochemical study of 2 cases.

Two cases of primary sebaceous lymphadenoma of the thymus are presented. The patients were a man and a woman 58 and 77 years old, respectively. The female patient had a history of breast carcinoma and on follow-up was identified to have an anterior mediastinal mass; the male patient did not have any history of malignancy, and the tumor was discovered during a chest radiographic evaluation when the patient presented with symptoms of fatigue, chest pain, and dyspnea. Histologically, both lesions were characterized by the presence of solid-cystic epithelial islands in a prominent lymphocytic background. The epithelial islands were haphazardly distributed in the form of small tubular structures with focal keratinization and groups of epithelial cells with clear cytoplasm, round nuclei and lack of mitotic activity in keeping with sebaceous cells. The presence of germinal centers in the lymphoid background was seen in both cases. Immunohistochemically, the epithelial component was positive for cytokeratin 8 (CAM5.2), cytokeratin 5/6, and for adipophilin in the sebaceous component. B- and T-cell markers were positive in the lymphoid component. Clinical follow-up in both patients showed that the 2 patients were well and alive 3 years after diagnosis. The cases herein presented expand the spectrum of salivary gland-type tumors in the mediastinum and raise awareness of lesions which are easily confused with other more common thymic tumors that have different prognosis and treatment implications.