Abstract

AY Ye, KL Bradley, H Kader, YK Liu, C Poh, T Thompson, J Wu, JH Hay

Ipsilateral radiation (RT) for tonsil cancers reduces toxicity compared to bilateral techniques. In the pre-human papilloma virus (HPV) era, unilateral radiation (URT) was associated with low risk of failure in the contralateral neck. The purpose of this study was to explore URT in treating HPV-positive tonsil cancers.

Charts of tonsil squamous cell carcinoma (SCC) patients treated with radical RT or radical chemoradiotherapy (CRT) between 2001 and 2007 were reviewed. HPV status was determined through p16 immunohistochemistry. RT was mainly either 70Gy in 35 daily fractions or 60Gy in 25 daily fractions. Chemotherapy was mainly q3 weekly high-dose Cisplatin or Carboplatin-based.

Of 405 retrievals, 83 were excluded due either to classification errors, not receiving treatment at the agency or non-curative intent treatment; 140 were excluded because p16 status could not be determined. Of the 182 subjects reviewed, 142 (78%) were p16 positive. Bilateral RT (BRT) was delivered to 63 and 58%; and CRT was delivered to 42 and 28%, of p16 positive and negative subjects, respectively (statistically similar). With a median follow-up of 49 months, response and recurrence rates were similar between the two groups with 81 and 88% achieving a complete clinical response post-RT or CRT; and 20 and 25% developing a recurrence. Despite similar LRC and DFS, there was a significant survival benefit seen in p16 positive subjects, with a 3 yr OS rate of 85% vs. 64% (p=0.02). Overall rates of contralateral recurrence (CLR) were low (3%). Among those who received URT, CLR rates were similar (7.5% vs. 5.9%, p=0.91). There was no difference in LRC, DFS or OS among this subset. Among p16 positive subjects, CLR rates were 7.5% for those treated with URT, and only 1.1% for those treated with BRT, p=0.05. Of the 4 p16-positive subjects treated with URT, three were treated with neck dissection (one cured, one died of lung metastases, and one died of a separate malignancy); and one received palliative radiation to the neck and distant metastatic site.

The association between HPV-positive tonsil SCC and improved survival outcomes, despite more advanced nodal stage is confirmed. While CLRs remain rare overall, there appears to be an 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.