65-year-old man with worsening shortness of breath   

History and images

Our appreciation is extended to Dr. Abdul Majeed Abid, University of Pittsburgh Medical Center (UPMC), for contributing this case.

History: A 65-year-old man with a past history of non-ST-elevation myocardial infarction presented to his primary care physician with worsening shortness of breath. Imaging revealed an incidental anterior mediastinal mass with poorly defined, irregular lobular margins. A needle biopsy was performed on the mass. Click on images to enlarge.

What is the top differential diagnosis?
T cell lymphoma
Squamous cell carcinoma

What stains would favor a thymic origin compared to other sites?
P40, TTF1
S100, SOX-10
CK19, CD5
CD5, CD117