Thymoma with nuclear expression of thyroid transcription factor-1: a potential diagnostic pitfall on core biopsy.

The clinicopathologic features of the first case of a thymoma with a strong nuclear expression of thyroid transcription factor-1 are reported. The thymoma was classified as type AB according to the WHO-system. No definitive correlation between the different histologic patterns or neoplastic cell types and thyroid transcription factor-1 expression was discerned. No immunohistochemical evidence of neuroendocrine differentiation was identified with synaptophysin, chromogranin A, and CD56.