Usefulness of Immunocytochemical Staining for Brachyury in Cytodiagnosis of Conventional Chordoma

Background/Objectives: Conventional chordomas are rare malignant bone tumors characterized by brachyury expression. The presence of polygonal-to-epithelioid neoplastic cells containing rich cytoplasm and relatively large nuclei in a myxoid background is a characteristic cytological feature of conventional chordomas. Physaliphorous cells, characterized by the presence of multiple well-marginated vacuoles within the cytoplasm, are also characteristic of this rare bone tumor. However, the cytological diagnosis of conventional chordomas can be challenging because of their rarity and lack of specific features. Therefore, useful immunocytochemical markers are required. Immunohistochemical staining for brachyury has been widely used for diagnosis; however, immunocytochemical staining using cytological specimens has not yet been performed. The purpose of this study was to evaluate the usefulness of the immunocytochemical staining for brachyury in cytodiagnosis of conventional chordoma. Methods: This study included patients diagnosed with conventional chordoma based on postoperative histopathological findings who underwent intraoperative squash cytological examination. Cytological features and immunocytochemical staining for brachyury were evaluated. Results: Two patients with conventional chordoma were included. The tumor extended from the lumbar spine to the cauda equina and clivus. Cytological examination revealed the presence of small sheets and isolated polygonal neoplastic cells with rich cytoplasm and round nuclei with inconspicuous nucleoli in a myxoid background. Cellular clusters were noted in one specimen and physaliphorous cells were observed in the other. Immunocytochemical staining for brachyury revealed positive nuclear expression in both specimens. Conclusions: Immunocytochemical staining for brachyury could provide useful information for the cytodiagnosis of this rare tumor, even in cases lacking typical cytological features.