(P 146) LOCALISED CHONDROSARCOMA PERIOPERATIVE TREATMENT: REAL-WORLD OUTCOMES AND CHALLENGES ACROSS HISTOLOGIC SUBTYPES

Objective: Surgical resection remains the cornerstone of chondrosarcoma (ChS) treatment; however, the role of chemotherapy (CHT) and radiotherapy (RT) is less well defined, particularly in high-grade and rare variants. We aimed to evaluate the impact of multimodal treatment (MDT) in a perioperative setting in marginally resectable chondrosarcoma (ChS); and describe perioperative complications of MDT treatment.

Methods: We retrospectively analysed patients(pts) with a confirmed diagnosis of localized ChS treated between 1998 and 2025. Median overall survival (mOS) and median relapse-free survival (mRFS) were calculated with Kaplan-Meier and prognostic factors were assessed with a log-rank test. Surgery complications were described with Clavien-Dindo scale (C-D).

Results: 27 ChS pts were enrolled in the study with dedifferentiated (DD)ChS in 9 pts (33.3%), mesenchymal (M)ChS in 8 (29.6%), and conventional (C)ChS in 8 (29.6%). Primary ChS tumors were most often located in lower extremity (n=13; 48.1%), and trunk (n=7; 25.9%). CHT was administered as neoadjuvant in 16 pts (59.3%), adjuvant - in 17 pts (63%). Neoadjuvant RT was administered in 6 pts (22.2%) and as adjuvant in 4 (14.8%). We performed surgery with reconstruction in 16 pts (59.3%), endoprosthesis implantation in 7 pts (25.9%), while in 11 pts (40.7%) limb amputation was necessary. R0 margins were achieved in 19 pts (70.4%), R1- in 7 (25.9%), and R2 in 1 (3.7%). In the entire cohort, mRFS was 10.6 months(mo) with the 3- and 5-year RFS rates of 36% and 22.5%, respectively. mOS was 40.8 mo (3-; 5-year OS: 50.4%, 40.8%). Only 4 pts (14.8%) had an uneventful postoperative course. We reported C-D complications of Grade I–II in 14 pts (51.9%) and ≥ Grade IIIA in 5 pts (18.5%).

Conclusion: Localised ChS remains a therapeutically challenging malignancy, with modest long-term survival and high relapse rates despite multimodal treatment. Achieving R0 surgical margins was feasible in the majority of pts and remains critical for disease control. Postoperative complications were frequent, with a significant proportion of pts experiencing moderate to severe surgical morbidity. There is an urgent need for optimised surgical strategies and the development of effective systemic therapies for ChS.