Palliative Stereotactic Body Radiotherapy for Metastatic Clear Cell Sarcoma: A Case Report.

Clear cell sarcoma (CCS) is an extremely rare malignancy. We report a case of metastatic CCS in which pain was successfully relieved with palliative stereotactic body radiotherapy (SBRT). The patient was a 57-year-old man diagnosed with CCS of the right heel five years prior. He had undergone seven surgical resections and chemotherapy (trabectedin and pazopanib) for the primary tumor and metastatic lesions. While receiving trabectedin therapy, he was referred to our facility for palliative radiotherapy. This was due to the rapid enlargement of a metastatic lesion in the right thigh. His symptom was pain in the right lower extremity. Metastatic lesions in the right thigh and right abdomen were targeted for SBRT. SBRT was delivered every other day using an O-ring linear accelerator (OXRAY) with 6-MV flattening filter-free beams, volumetric modulated arc therapy, and image-guided radiotherapy (IGRT) (thigh: treatment volume 319.57 mL, prescribed dose (the dose covering 95% of the target volume; D95) 30 Gy in 5 fractions, maximum dose 67.05 Gy, irradiation time 324 seconds/fraction, treatment duration 10 days; abdomen: treatment volume 36.2 mL, prescribed dose (D95) 36 Gy in 3 fractions, maximum dose 51.92 Gy, irradiation time 293 seconds/fraction, treatment duration five days). By the fifth day of SBRT, the pain in the right lower extremity completely resolved. Shrinkage of the right thigh metastasis was observed on cone-beam computed tomography (CT) scans of IGRT during the treatment period. CT imaging performed seven weeks after SBRT showed further shrinkage of both lesions. The pain did not recur until the patient died of renal failure two months after SBRT. No adverse events occurred during the clinical course. SBRT may be a viable palliative treatment option for CCS.