Dedifferentiated chordoma: a case report.

Dedifferentiated chordoma, i.e. chordoma with a sarcomatous component, is a rare bone tumor. This case report is of a dedifferentiated chordoma in the sacrococcygeal region in a 50-year-old male. The patient was initially diagnosed as having a leiomyosarcoma at the first medical consultation, but after the tumor recurred it was proven to be a dedifferentiated chordoma. The primary tumor, which measured 7 x 5 cm, was located in front of the sacrum so as to compress the rectum forward. The resected specimen showed histological features of chordoma, but the presence in some parts of the tumor of spindle-shaped epithelial cells led to a misdiagnosis of leiomyosarcoma. Thirty-six months later, a local recurrent tumor measuring 24 x 17 cm was identified and promptly resected. The recurrent tumor showed features of pleomorphic cell sarcoma mimicking malignant fibrous histiocytoma. In the pleomorphic sarcomatous area, many mitotic figures were seen, and the MIB-1 labeling index was greater than 40%, which was higher than that of the conventional chordoma area. From histological and immunohistochemical examination, the resected tumor was proven to be a dedifferentiated chordoma. This case highlights the importance of careful study of suspected chordoma to allow early identification of sarcomatous components. When we encounter a chordoma with a spindled epithelial component, we need to distinguish this tumor from a dedifferentiated chordoma and other spindle cell sarcomas such as leiomyosarcoma.