Chordoma : Brachyury
Chordoma - Immunophenotype: Chordomas express brachyury, cytokeratin AE1/AE3, EMA, S100 protein, SOX9 and vimentin. CEA and GFAP are variably positive. With GFAP, reactivity is usually seen with polyclonal antibodies and less often with monoclonal antibodies. Poorly-differentiated chordomas show loss of SMARCB1/INI1 staining. Brachyury, a nuclear transcription factor encoded by the TBXT gene, is a highly sensitive and specific marker for chordomas. Brachyury regulates the development of notochord-derived tissues and also plays a role in the pathogenesis of chordomas. It is not expressed in chondrosarcomas, myoepitheliomas and other mimics of chordomas. Brachyury immunoreactivity may be lost following decalcification. Poorly-differentiated and de-differentiated chordomas can also be negative for brachyury. Brachyury is positive in a few other neoplasms; however, none of them resemble chordoma microscopically and do not enter into the differential diagnosis.