A Simple Grading Scale Incorporating Age and Arterial Encasement to Predict Progression-Free Survival in Skull Base Chondrosarcoma

Background: Skull base chondrosarcomas frequently involve critical neurovascular structures that make complete resection challenging. Because chondrosarcomas are uncommon, predictors of tumor progression in the skull base as unknown.

Methods: We performed a retrospective analysis of patients treated for skull base chondrosarcoma at the University of Pittsburgh from 2004 to 2018, which included 43 patients. We recorded locations involved along the skull base (petroclival, sublacerum, cavernous sinus, posterior clinoids, and orbit/anterior fossa) and radiographic tumor features (size, intradural extension, enhancement, calcification, number of major arteries encased). Major arteries included internal carotid, basilar, and vertebral arteries and had to be compressed or at least 50% encased. Our primary outcome was progression-free survival (PFS). Univariate and multivariate regression models were created.

Results: Of 43 patients treated for skull base chondrosarcoma, the mean age was 52 years, 60.5% were female, and mean follow-up was 55 months. Gross-total and near-total (>95%) resections were achieved in 60.5 and 79.0%, respectively. For the entire cohort, the median PFS was 123 months ([Fig. 1]).

Among clinical features, only older age was correlated with shorter PFS (p < 0.017). We performed univariate regression analysis of involved tumor locations ([Fig. 2A]) and of radiographic parameters ([Fig. 2B]) for each tumor. Those parameters with a p-value of < 0.1 were fed into a Cox proportional hazards model. This multivariate regression revealed an independent association of both age (p < 0.018) and increasing number of arteries encased (p < 0.045) with PFS ([Fig. 2C]). When we subdivided by age, we found that the youngest quintile <35 years did not progress in our cohort, whereas the median PFS in patients over 60 years was half that of those 35 to 60 years of age (63 vs. 123 months, respectively) ([Fig. 3A]). When comparing PFS in tumors that encased 0–2 versus 3–4 major arteries, median PFS was dramatically reduced (127 vs. 48 months, respectively) ([Fig. 3B]).

We next generated a simple grading scale based on both independent variables: age and number of encased arteries ([Fig. 4A]). Age < 35 years was given 0 points, and age > 35 years was given 1 point. If 0–2 major arteries were encased, this was given 0 points, but three to four encased arteries were given 1 point. Importantly, the median PFS in patients with a total score of 2 was half that of those with a total score of 1 (48 vs. 97 months, respectively), whereas patients with a total score of 0 never progressed in our cohort ([Fig. 4B]).

Conclusion: In patients with skull base chondrosarcomas, age and artery encasement predict prognosis useful and may help guide postoperative follow-up and adjuvant therapy.