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Case of the Month



Spindle Cell Thymoma

A 54 year old man with no significant past medical history presents with chest pain, fever, and cough. A 9.5 cm sharply circumscribed, tan-yellow, solid mass was resected from the anterior mediastinum.  The cut surface was divided into vague lobules by delicate fibrous bands. Histologically, the tumor was comprised of a monotonous population of oval to spindle shaped cells arranged in a storiform pattern.  The nuclei demonstrated stippled, uniformly distributed chromatin and small, inconspicuous nucleoli.  Mitoses were rare. 

There was no necrosis.  Scattered lymphoid cells were present.  Immunostain for cytokeratin (Cam5.2) was uniformly positive and for S100 protein was negative. 

A diagnosis of thymoma, WHO Type A (spindle cell thymoma) was rendered.  While thymoma represents the most common (20-50%) epithelial tumor of the anterior mediastinum, spindle cell thymoma is uncommon, accounting for 5-19% of all thymomas.  A recent review (Applied Immunohistochemistry & Molecular Morphology. 19(4):329-335, July 2011) summarizes the clinical, histochemical, and immunohistochemical features of the tumor.