(P 290) OSTEOSARCOMA OF THE HEAD AND NECK (HN) IN ADULTS: A CANSARCC STUDY

Objective: The aim of the study is to describe the oncological experience of head and neck osteosarcoma (HNO) in Toronto referral tertiary cancer centers to investigate the parameters that may influence outcome.

Methods: After ethics board approval, data from patients with a diagnosis of HNO between the years 1996-2021 were extracted from the CanSaRCC (Canadian Sarcoma Research and Clinical Collaboration) Database. Patients' baseline characteristics, treatment and outcomes were analyzed. Univariate (UVA) and multivariate (MVA) Cox regression models were computed for variables correlating to outcomes. 5-year recurrence-free survival (RFS) and 25-year overall survival (OS) were estimated using Kaplan-Meier method and Log-Rank test. T-test, ANOVA and Wilcoxon rank were used to compare means and medians between groups. Chi-square and Fisher’s test were used to compare demographic features. A threshold analysis for optimal closest margins was performed using Kaplan-Meier for both OS and RFS.

Results: Of 52 patients with a median age of 39.9 years (range 17-80), 28 (53.8%) were male. Osteosarcoma was commonly involving the mandible (n=22, 42.3%) followed by maxilla (n=15, 28.8%). Clinical and demographic data are presented in Table 1. Forty-nine patients (94.3%) had surgery, of them, 78.7% (n=37) were R0 resection. Three patients (5.8%%) had negative margins above 5mm, 24 patients (46.2%) had close margins between 1-5mm, 15 patients (28.8%) had positive margins lower than 1mm and 7 patients had unknown margins. Twenty-two patients (42.3%) received neoadjuvant chemotherapy while 17 patients received adjuvant chemotherapy. A total of 13 patients (25%) received radiotherapy (RT): 9 (21.4%) patients received post-operative and 3 patients received pre-operative. Of those who received post-operative RT, 6 patients had positive resection margins (lower than 1mm), 2 patients had 2mm closest margins and one patient had unknown margins. The Median follow-up time was 5.76 years (range 0.07-24.89). Disease recurrence was noted in 22 patients (42.3%). ). Of them, 16 patients (72.2%) had local recurrence, 4 patients had distant metastasis, and 2 patients had both local and distant recurrence. 5-year RFS and 25-year OS were 59.6% and 67.3% respectively. Table 2 presents patients' outcome. Survival analysis of patients with closest margins below 3mm showed lower 25 years OS and RFS compared to patients with closest margins above 3mm (Log-Rank p=0.02, p=0.01 respectively (Figure 1 and Figure 2). Residual tumor classification (R status) was not a prognostic factor for survival. By UVA, patients diagnosed with radiation induced sarcoma (RIS) had a lower OS rate (p< 0.001, HR=3.8, 95% CI 1.4-10.5). In addition, patients with high grade had a lower RFS rate (p=0.04, HR=4.73 CI 95%1.07-20.9). RT or Neo-adjuvant chemotherapy did not influence RFS or OS.

Conclusion: Osteosarcoma is a rare head and neck cancer entity in which local recurrence remains a concern. Surgical resection with negative margins of at least 3mm may improve RFS and OS rates. Radiotherapy or Neo-adjuvant chemotherapy was not associated with improved recurrence free survival or overall survival and should be considered in select cases in a multidisciplinary setting.