(P 164) LONG TERM OUTCOMES IN PATIENTS DIAGNOSED WITH SECONDARY CHONDROSARCOMA

Objective: Secondary chondrosarcoma (SChS), arising from pre-existing benign cartilaginous lesions such as osteochondromas, is a rare malignant tumour with limited evidence guiding optimal surgical management and prognostication. We aim to evaluate the clinical outcomes, prognostic factors, and surgical complication profile in patients with SChS, with a particular focus on the impact of resection margin status on relapse-free and overall survival.

Methods: Patients(pts) with a confirmed diagnosis of SChS were included in a retrospective analysis. Median relapse-free survival (mRFS) and median overall survival (mOS) were analysed using the Kaplan-Meier; log-rank test was used to assess potential prognostic factors; Clavien-Dindo scale - to classify surgical complications.

Results: The cohort included 31 pts, predominantly male (67.7%), with a median age of 35.7 years (range: 18.5–71.3). Predispositions included solitary osteochondroma (n=21, 67.7%), hereditary multiple osteochondromas (HMO; n=3, 9.7%), enchondroma (n=2, 6.5%), Ollier’s disease (n=1, 3.2%); in 4 pts (12.9%) no specific predisposition was diagnosed. Tumours were located predominantly in the lower extremities (n=19, 61.3%), followed by the trunk (n=10, 32.3%) and upper extremities (n=2, 6.5%). Subtypes included: peripheral (n=27, 87.1%) and central (n=4, 12.9%). Grades were: G1 (n=27, 87.1%) and G2 (n=4, 12.9%). All pts underwent primary SChS resection with endoprosthesis implantation (n=7, 22.6%), hemipelvectomy (n=3, 9.7%). Resection margins were R0 (n=18, 58.1%), R1 (n=9, 29%), and R2(n=1, 3.2%). Surgical complications were recorded in 19 pts (61.3%), with Clavien-Dindo grade ≥ IIIA in 8 pts (25.8%). mRFS was 10.2 months (95% CI: 110.2–NA), with 5-year RFS and OS rates of 76.7% and 92.2%, respectively. mRFS was 10.2 months (95% CI: 110.2–NA), with 3- and 5-year RFS rates of 86.1% and 76.7%, respectively. mOS was 110.2 months (95% CI: 97.1–NA), with a 5-year OS rate of 92.2%. Pts with R0 resection showed improved mRFS and mOS compared to those with R1 or R2 resections.

Conclusion: Resection with negative margins (R0) remains the most important determinant of improved RFS and OS in SChS pts. Despite a high incidence of surgical complications, long-term prognosis is favourable and local control achieved in most pts with SChS.