[Dedifferentiated chordoma of sacrococcygeal region: a clinicopathologic analysis and review of literature].

Objective: To study the clinicopathologic features of dedifferentiated chordoma. Methods: Four cases of dedifferentiated chordoma of sacrococcygeal region were collected at Beijing Jishuitan Hospital, from 2009 to 2014. HE and immunohistochemistry (EnVision method) were used to observe the clinical, radiological and histological features of dedifferentiated chordoma and to make the diagnosis and differential diagnosis. The literature was reviewed. Results: Four cases of dedifferentiated chordoma were all located in the sacrococcygeal region. The mean age at diagnosis was 57 years (range 49-64 years). There were 1 female and 3 males. Histologically, there were two components of conventional chordoma and dedifferentiated sarcoma with or without transitional area between them. The histology of dedifferentiated components includes undifferentiated sarcoma and fibrosarcoma. Immunohistochemical study showed that cytokeratin, epithelial membrane antigen, S-100, Brachyury were positive in the portion of chordoma while p53 were positive in the portion of undifferentiated sarcoma. INI1 and vimentin were both positive. Conclusions: The dedifferentiated chordoma is very rare. The diagnosis should combine the histological characters and immunohistochemical results and should be differentiated from the sarcomatoid chordoma, poorly differentiated chordoma and other high grade sarcoma. p53 may play a role in the malignant transformation mechanism of chordoma.