Figure 14.

Thymic squamous cell carcinoma (A,B) and NUT carcinoma (C-F). (A) Irregular nests of tumor cells are within a fibrotic stroma and invade adjacent adipose tissue. (B) The tumor cells are large, have round nuclei with more conspicuous nucleoli, and grow in a desmoplastic stromal reaction. The tumor cells are positive for p40 and negative for NUT and EBV in situ hybridization (not shown). (C) Sheets of neoplastic cells and large areas of necrosis are present. (D) The neoplastic cells have a monotonous cytology characterized by round-to-slightly-oval cells with only a small amount of cytoplasm and conspicuous nucleoli. There is an abrupt squamous differentiation. The tumor cells are positive for p40 (E) and NUT (F) (note the characteristic stippled nuclear staining pattern of NUT). Magnification, H&E ×2 (A), ×40 (B), ×100 (C), ×400 (D), p40 ×400 (E), NUT ×400 (F). NUT, nuclear protein in testis; EBV, Epstein-Barr virus; H&E, hematoxylin-eosin.