Parachordoma exists--but what is it?

Parachordoma is a very rare peripheral soft tissue tumor of unknown lineage, which has been described under other names, all of which imply a similarity to chordoma. It forms a circumscribed firm tumor, usually in deep soft tissue, with a variety of histologic patterns and cytologic features, including cords and nests of cells, some of which are vacuolated. The ultrastructure and immunophenotype indicate epithelial differentiation and parachordomas are additionally S-100 protein positive. This tumor is distinct from extraskeletal myxoid chondrosarcoma and probably from soft tissue myoepithelioma. While histologically it somewhat resembles chordoma, parachordoma has a wider range of appearances, and the two neoplasms differ in their detailed cytokeratin immunophenotype and their clinical behavior. Parachordoma is a slowly growing tumor with occasional late recurrence; cases with reported metastasis have not been histologically convincing. This commentary discusses the terminology, origin, and possible nature of this enigmatic neoplasm.