Basaloid Squamous Cell Carcinomas of the Thymus With Prominent B-Cell Lymphoid Hyperplasia

Ten cases of basaloid squamous cell carcinomas of the thymus are presented. The patients are 6 women and 4 men ranging in ages between 51 and 72 years (average: 61.5 y), who presented with nonspecific symptoms of cough, dyspnea, and chest pain with no history of malignancy, myasthenia gravis, or other autoimmune disease. Surgical resection of the mediastinal masses via thoracotomy or sternotomy was performed in all patients. Grossly, the tumors varied in size from 2 to 8 cm, were light tan in color, solid and slightly hemorrhagic, and had infiltrative borders. Histologically, scanning magnification showed elongated interanastomosing ribbons of tumors cells embedded in a lymphoid stroma containing germinal centers. At higher magnification, the tumors cells were round to oval with moderate amounts of lightly eosinophilic cytoplasm, oval nuclei, moderate cellular atypia, and mitotic activity ranging from 3 to 5 mitotic figures per 10 HPFs. In 8 cases, the tumor invaded perithymic adipose tissue, in 1 case the tumor infiltrated pericardium, and in 1 case, the tumor involved the pleura. Immunohistochemical stains showed positive staining in the epithelial component for pancytokeratin, p63, keratin 5/6, and p40, while CD20 and CD79a characterized the lymphoid component. Clinical follow-up was obtained in 7 patients. Two patients died within 24 months and 5 patients remained alive between 12 and 60 months. The current cases highlight the unusual feature of B-cell lymphoid hyperplasia in these tumors and their potential aggressive behavior.