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Chondrosarcoma - Sarcoma of the Year

(P 151) SHOULD WE USE ADJUVANT CHEMOTHERAPY IN PATIENTS WITH LOCALIZED DEDIFFERENTIATED CHONDROSARCOMA (DDCS) OF THE PELVIS? AN ANALYSIS BY THE PELVIC DDCS STUDY GROUP

Objective: Dedifferentiated chondrosarcoma (DDCS) accounts for up to 1-2% of all chondrosarcomas, it is associated with poor prognosis, and presents PDL1 positivity in 20 - 40% of the cases. 5-year survival rates range from 7% to 24% with worse outcomes in pelvic primary location. Recently, a consensus on the use of adjuvant chemotherapy in patients with DDCS was reached, while data are limited in the pelvis. Here we report an analysis on neoadjuvant or adjuvant chemotherapy (adj-CT) from the pelvic DDCS Study Group.

Methods: Multicenter retrospective cohort study from 35 orthopedics oncology centers. Period of study: 1985-2022. A subgroup analysis on 240/297 DDCS patients with localized disease was performed. Progression-free survival (PFS) and Overall survival (OS) were evaluated using Kaplan-Meier curves and Cox regression, stratified by the use of adj-CT.

Results: 86/240 (35%) of the patients underwent adj-CT and were younger than those who did not. Median PFS and OS were 10.7 and 20.1 months, respectively, with no significant difference by adj-CT use (median PFS adj-CT No 10.4 months, adj-CT Yes 11.1 months, p 0.67).
After multivariable analysis, separate Cox models showed that R1 and R2 positive margins were associated with worse PFS and OS. Male sex was associated with worse PFS in both models (aHR = 1.47, p = 0.01).

Conclusion: This retrospective review did not observe a statistically significant superiority of adj-CT in patients with pelvic DDCS. R1 and R2 margins and identification as male were associated with poorer PFS. Due to PDL1 expression, further studies evaluating adjuvant immune checkpoint, combined with radiotherapy (proton or other), and adj-CT, are warranted.

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