65-year-old man with worsening shortness of breath   

Findings and diagnosis


Microscopic description

Histologic sections show infiltrative sheets, islands, and cords of large polygonal cells, accompanied by broad zones of desmoplastic stroma. Tumor islands are traversed by delicate blood vessels. The tumor is poorly differentiated. On immunohistochemistry, CD5 was patchy positive. CD117/c-KIT, PAX-8, and p40 were diffusely positive. TdT, CD3, CD20, and CK20 were negative. This immunoprofile is consistent with a squamous cell carcinoma, most likely of thymic origin.

Differential diagnosis

  • Pulmonary squamous cell carcinoma
  • Thymoma type B3
  • Atypical carcinoid
  • Lymphoepithelial carcinoma
  • Thymic carcinoma

Diagnosis: Thymic carcinoma