Patterns of Relapse in Squamous Cell Carcinoma of the Tonsil - Unilateral vs. Bilateral Radiation in the HPV-Era

Objectives: In the pre-human papillomavirus (HPV) era, unilateral radiation therapy (URT) for tonsil cancer was associated with low contralateral failure rates and had less toxicity than bilateral radiation therapy (BRT). This study explores the validity of URT in HPV-positive tonsil cancers. Methods: Tonsil squamous cell carcinomas (SCC) treated (typically with 70 Gy radiation and Cisplatin-based chemotherapy) between 2001 and 2007 were reviewed. Retrospective p16 immunohistochemistry staining was undertaken. Baseline, treatment, and response data were collected. Results: Of 182 patients, 78% were p16-positive, were younger (predominantly male), mostly former or non-smokers, and had a more advanced nodal stage. With a median follow-up of 68 months, contralateral recurrence (CLR) rates were low (3.5% p16-positive versus 2.5% p16-negative, p=0.63). Overall survival (OS) was 74% for p16-positive versus 54% for p16-negative subjects (p=0.01), but all other outcomes were similar. Analysis amongst only p16-positive subjects revealed URT was delivered to 37%, with CLR rates of 7.5% versus 1.1% for those treated with BRT, p=0.05. Of the four p16-positive subjects treated with URT who developed contralateral recurrences, three were managed with neck dissection (two disease-free and one died of lung metastases) and one received palliative radiation to the neck and distant metastatic site. All disease control and survival outcomes were similar between those treated with URT versus BRT. Conclusion: While CLRs remain rare overall, there appears to be a slightly increased rate among HPV-positive subjects treated with URT. However, overall outcomes do not appear to be impacted, suggesting that URT remains a reasonable approach in HPV-positive subjects.