Chondrosarcoma of the mobile spine: impact of tumor status at referral and surgical strategy on oncological outcome

BACKGROUND: Chondrosarcoma (CHS) is a rare malignant bone tumor, mostly histologically low grade, demonstrating limited response to chemotherapy and conventional photon radiotherapy (RT). According to Enneking Staging System, tumor-free margin en bloc resection is the cornerstone of treatment. When arising in the spine (around 10% of the cases), tumor-free margin en bloc resection is technically demanding, but intralesional excision has historically been associated with high recurrence rates. The role of Particle Therapy (PT) in combination with intralesional surgery to improve local control is a promising option, but still controversial. Many CHS are referred to spine oncology centres after inconsistent attempt of treatment with possible negative impact on the outcome. PURPOSE: The aim of this study is to evaluate the prognostic role of pre-operative tumor status and to compare the Local Recurrence-Free Survival (LRFS) after en bloc resection and after intralesional surgery, with or without conventional RT or PT, in patients with low grade CHS of the mobile spine. MATERIALS AND METHODS: A retrospective observational study was carried out on 91 treatments performed in 67 patients affected by low grade CHS of the spine in a tertiary referral center, by the same spine oncology team over the time span of 40 years. Forty-five surgeries were performed in tumors previously treated, defined as "not-intact", while 46 were treatment-naive and were defined "intact". Thirty-eight en bloc resections (two of them associated to PT) and 53 intralesional procedures (3 associated to conventional RT, 18 associated to PT) were performed. RESULTS: Out of 91 surgeries, the overall rate of local recurrence was 40.6%. Ten recurrences occurred on 46 "intact" tumors (21.7%), whereas 27 recurrences occurred among 45 "not-intact" tumors (60.0%). Kaplan-Meier survival analysis confirmed significantly worse LRFS in "not-intact" tumors (log-rank p < 0.001). Further, significantly improved outcomes were suggested after en bloc resection compared with intralesional procedures (log-rank p < 0.001). Local recurrence occurred after 5 on 38 en bloc resection, alone or combined with PT (13.1%) compared with 32 on 53 intralesional procedures alone or combined with conventional RT and PT (60.4%). In particular, association of PT to intralesional surgery is followed by 55.6% local recurrence rate (10 local recurrence on 18 cases): four-fold higher that en bloc surgery alone (5 local recurrence on 36, p = 0.0028) with Kaplan-Meier survival analysis demonstrating worse LRFS (log-rank p = 0.00043). CONCLUSION: Previously treated tumors were associated with significantly worse oncological outcomes. En bloc resection provided the best local control, whereas intralesional surgery showed higher recurrence rates even when combined with PT.