Outcomes for Oligometastatic Head and Neck Cancer Undergoing SBRT: Results From an International Multi-Institutional Consortium

Abstract

Treatment of oligometastatic disease with SBRT has shown the potential to improve disease control and survival in trials largely focused on lung and prostate cancer. Outcomes in other sites, such as head and neck cancers (HNC) are poorly defined. Here we report the results of a multi-institutional cohort of oligometastatic HNC patients receiving SBRT.Data on HNC patients treated between 2008 and 2016 was extracted from an international consortium of six high volume SBRT centers. Patients were considered oligometastatic if they had 5 or fewer extracranial metastases. The risk of local recurrence (LR) and widespread progression (WSP, defined as 6 or more metastatic sites) was estimated with competing risks analysis. Overall survival (OS) and progression-free survival (PFS) were estimated with the Kaplan-Meier method. Univariable and multivariable regression analysis (MVA) was used to determine the relationship between covariates and the main endpoints.Forty-two patients harboring 84 metastases from mucosal head and neck cancer were included. The median age was 64 and most patients were male (83%). The median follow up was 18.2 months. The most common primary site was the oropharynx (43%). Most patients had 1 or 2 metastases (78.6%). Metastatic sites treated with SBRT were mostly lung (50%) and bone (35.7%). Presentation was synchronous in 11 patients (26.2%), early metachronous (within 24 months of diagnosis, 57%) and late metachronous in 7 patients (> 24 months from diagnosis, 16.7%). The majority of patients (88%) had no systemic therapy prior to SBRT. SBRT dose and fractionation ranged from 20-28 Gy/1fx to 50 Gy in 5-10fx. The median biologic equivalent dose (BED10) was 100 Gy. The local control rate was 80% at 1 year and 66% at 2 years. The median PFS was 4.7 months. The median overall survival (OS) was 23.3 months. Improved local control on MVA was seen with patients who had a maximum point BED greater than the median (HR = 0.31; 95% CI: 0.10-0.91, P = 0.03). Disease burden significantly correlated with PFS, with larger combined PTV volumes for all metastases greater than the median of 48cc having worse PFS on MVA (HR = 2.99; 95% CI: 1.58-5.66, P < 0.001). The risk of WSP at 12 and 24 months was 31.7% and 48.3%, respectively. There was a trend towards lower rates of WSP for patients who presented with late metachronous disease versus all others (HR = 0.22; 95% CI: 0.03-1.82, P = 0.16). Severe toxicity was rare, with one patient developing a grade 3 brachial plexus injury after spine SBRT and one patient with grade 3 pneumonitis after lung SBRT.Patients undergoing SBRT for oligometastatic head and neck cancer have favorable local control and overall survival, however, PFS remains short. Patients with a late metachronous presentation may have more favorable biology. Future study should focus on whether subsets of patients such as those with synchronous or early metachronous disease may benefit from pre-SBRT systemic therapy.