Extra-axial dedifferentiated chordoma: A case report with brachyury immunohistochemical confirmation, literature review and pathologists’ perspective

Dedifferentiated chordoma is a rare and aggressive malignant bone tumor. It is known as a variant of conventional chordoma, which possesses additional high-grade sarcomatous elements. Dedifferentiated chordoma is commonly identified in axial location as recurrences, or following radiation therapy of primary tumors. Prognosis is poor and there is a potential risk for metastasis. There have been only a few reports of primary dedifferentiated chordoma. Owing to its rarity, especially when it is in an unusual extra-axial location, primary dedifferentiated chordoma presents a diagnostic challenge. Brachyury, a recently described immunohistochemical marker specific for chordoma, has improved the diagnostic accuracy of chordoma and its variants in extra-axial sites. We herein report an exceptional case of extra-axial dedifferentiated chordoma confirmed by the expression of brachyury, the first case report of this kind. The review of relevant literature and discussion of practical diagnostic approach from sarcoma pathologists’ perspective are intended to provide an update of this topic.