Sarcomatous transformation of clival chordoma after charged-particle radiotherapy. Report of two cases.

Skull base chordomas containing a sarcomatous component are extremely rare. Here the authors report two new cases in which a recurrent tumor with a sarcomatous component appeared after the patient had undergone charged-particle radiotherapy. Histological examinations performed in Case 1 revealed some retention of epithelial features in the sarcomatous component, whereas no such regions were observed in Case 2. Both patients had rapidly deteriorating clinical courses and died within 6 months after diagnosis of the recurrent tumor. The authors discuss the significance of the histological subtypes of these tumors for long-term prognosis and their pathogenetic mechanisms in relation to radiotherapy. Although these sarcomatous transformations are rare in conventional chordomas, a careful histological examination and thorough follow-up imaging studies are crucial when treating patients with such lesions.