Postoperative radiotherapy in patients with extracranial chondrosarcoma, a joint study of the French Sarcoma Group and Rare Cancer Network.

Abstract: Background Postoperative radiotherapy (poRT) of intracranial/skull base chondrosarcomas is standard treatment. However, consensus is lacking for poRT in extracranial CHS (eCHS) due to easier resectability and intrinsic radioresistance. We assessed practice and efficacy of poRT in extracranial CHS. Patients and methods This multicentric retrospective study of the French Sarcoma Group / Rare Cancer Network included patients with eCHS operated on between 1985 and 2015. Inverse propensity score weighting (IPTW) was used to minimize poRT allocation biases. Results Of 182 patients, 60.4% had bone and 39.6% soft-tissue eCHS. eCHS were of conventional (31.9%), myxoid (28.6%, 41 extraskeletal (EMC), 11 skeletal), mesenchymal (9.9%), or other subtypes. En-bloc surgery with complete resection was performed in 52.6% and poRT in 36.8% of patients (median dose 54 Gy). Irradiated patients had unfavorable initial characteristics, with higher grade and incomplete resection. Median follow-up time was 61 months. Five-year incidence of local relapse was 10% with poRT vs 21.6% without (p=0.050). Using IPTW method, poRT reduced the local relapse risk (HR 0.27, 95% CI [0.14; 0.52], p Conclusion poRT should be offered in eCHS patients with high grade or incomplete resection, regardless of histological subtype.