A case of pelvic fusion sarcoma treated with carbon ion radiotherapy.

fusion sarcoma is a type of round-cell sarcoma with fusion that was newly categorized in the 2020 World Health Organization classification of soft tissue and bone tumors. In general, local disease is managed via surgical resection; however, at present, there is no standard therapy for locally advanced or metastatic disease. Here, we report our experience with a middle-aged male patient with pelvic fusion sarcoma who was treated with carbon ion radiotherapy and maintained stable disease for 13 months. The patient's clinical course suggests that carbon ion radiotherapy may be effective in patients with locally advanced fusion sarcoma.