The Effect of Upfront Radiation on Intermediate Grade Skullbase Chondrosarcomas

Background: Chondrosarcoma of the skull base is a rare and indolent but invasive malignancy that arises from the chondrocytes of the synchondroses of the skull. These are rare tumors, occurring at a rate of 0.2 per 100,000 people. Chondrosarcomas can be WHO grades 1–3. The cornerstone of treatment in all grades is maximal safe resection. In terms of adjuvant therapies, chemotherapy has been shown to be minimally effective, and the use of radiation remains controversial. These tumors are relatively radioresistant, and a high dose must be used to be effective, putting patients at risk of significant adverse effects when used. Radiation has been shown to effective in improving progression free survival in higher grade tumors and has thought to be useful in subtotal resection. The role of upfront radiation in intermediate grade tumors that have undergone gross total resection is unclear. Methods: We performed a retrospective analysis of patients who have undergone surgery for skull base chondrosarcoma at Mayo Clinic. We first described the tumor characteristics and clinical course for all tumors and then narrow to grade 2 tumors and consider the effect of radiation and extent of resection on patient outcome. Results: A total of 45 patients underwent resection of a skull base chondrosarcoma. Twenty-eight patients (62.2%) of the tumors were grade 2. Most patients (33, 73.3%) underwent open craniotomy; the remainder underwent endoscopic surgery. Gross total or near total resection was achieved in 48.9% of patients. Recurrence occurred at a rate of 22.2% and mean progression free survival was 64.7 ± 72.6 months. Amongst the 28 grade 2 tumors, 42.9% were gross totally resected or near totally resected. Progression free survival was 57.1 ± 70.7 months. Recurrence occurred at a rate of 21.4%. In multivariate logistic regression, when controlling for extent of resection, upfront radiation portended 0.038 times lower odds of recurrence (p = 0.037). In the 12 patients who underwent gross total resection, 2 patients were radiated up front, and neither had recurrence. Of the ten patients who did not undergo upfront radiation, 3 had recurrence for a rate of 30%. There was no statistically significant difference in rates of recurrence between the radiated and non-radiated patients (p=.3711). Of the 16 patients who had subtotal resections, 13 patients were radiated upfront and 1 recurred for a rate of 7.7%. Of the 3 that were not radiated upfront, 2 recurred for a rate of 66.7%. The difference between these groups was significant ( p = 0.018). Conclusion: In grade 2 tumors, there was a statistically significant difference in preventing recurrence in patients that were radiated upfront when the resection was subtotal, but no difference when the resection gross or near total. It is reasonable to monitor for recurrence with radiating in intermediate grade tumors that were completely resected. Publication History Article published online: 27 February 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany