Association of Cartilage Cap Thickness With Tumor Grade and Outcomes in Secondary Chondrosarcoma

Although increased cartilage cap thickness (CCT) is associated with secondary chondrosarcoma in patients with osteochondroma, no studies have assessed its relationship with histologic grade or outcomes after primary resection. Thus, the objectives of this study were to determine whether CCT is associated with (1) histologic grade in secondary chondrosarcoma and (2) oncologic outcomes after primary resection of secondary chondrosarcoma.

Patients who had a history of osteochondroma and were diagnosed with a biopsy-proven secondary chondrosarcoma at a single institution between January 2000 and December 2023 were included. CCT was measured on T2-weighted imaging or through direct measurement of the resected gross specimen. The primary outcome measure was of histologic grade. Secondary outcome measures were overall survival, local recurrence, distant recurrence, and margin positivity. Grade and margin positivity were evaluated using logistic regression models; time-to-event outcomes were assessed using Kaplan-Meier and cumulative incidence methods and Cox models.

Forty-five patients (30 male; median age, 39 years) were included. Thirty (67%) had grade 1 secondary chondrosarcoma, 12 (27%) had grade 2, and 3 (6.7%) had grade 3. Mean CCT was smaller in grade 1 chondrosarcoma (35 mm; SD, 18 mm) than in grade 2 or 3 disease (76 mm; SD, 30 mm; P < 0.001). Thicker cartilage cap was associated with increased odds of high (grade 2 or 3) versus low histologic grade (odds ratio, 1.11; 95% confidence interval, 1.05 to 1.21; P < 0.001). No statistically significant associations were observed between CCT and overall survival, local recurrence, distant recurrence, or margin positivity.

Although CCT may be a useful diagnostic marker for secondary chondrosarcoma, thickness itself is not a reliable prognostic marker for predicting long-term patient outcomes. However, its positive association with tumor grade may have implications for surgical planning.

Diagnostic Study.

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