The tumor cells are positive for pankeratin markers and express CK19, CK5/6, CK7, CK8 and CK10, but are negative for CK20. They are also positive for CD57, p63, PAX8 and EMA (focal). CD5 and CD117 (markers of thymic carcinoma) are usually negative. The background lymphocytes are immature T-cells which are TdT+, CD1a+, CD3+, CD4+, and CD8+. The image shows abortive Hassall corpuscles which are commonly found in type B3 thymomas. This tumor was found in a 45 year old man who presented with worsening cough, dyspnea, and chest pain. A large tumor was detected in the anterior mediastinum on imaging studies.