Risk of Post-Operative, Pre-Radiotherapy Contralateral Neck Recurrence in Patients Treated with Surgery Followed by Adjuvant Radiotherapy for Human Papilloma Virus-Associated Tonsil Cancer.

Objective: One approach to reduce treatment-related morbidity for human papilloma virus (HPV)-associated tonsil cancer is omitting radiotherapy to the contralateral neck. Pathologic risk factors for early contralateral neck disease, however, are poorly understood. We reporton the risk contralateral neck failures from the time of pre-operative diagnostic imaging to time of planning for adjuvant radiation in a single institution series of HPV-associated tonsillar cancer patients undergoing surgery followed by radiotherapy (RT). Methods: Retrospective analysis of 123 patients with T1-T3 HPV-positive tonsillar squamous cell carcinoma treated between 2010 and 2016 with transoral roboticsurgery and selective ipsilateral neck dissection followed by adjuvant RT. Contralateral neck recurrence was classified as the detection of a pathologic node in the contralateral neck prior to initiation of adjuvant RT. Results: Seven patients (5.7%) developed contralateralneck disease/failure between the time of pre-operative diagnostic neck imaging and time of planning of adjuvant radiation. Increased ratio of positive/resected nodes [odds ratio (OR) 1.073, p = 0.005] was significantly associated with increased risk of contralateral neck recurrence, with a trend found for close/positive margins (OR 5.355, p = 0.06), tumor size (OR 2.046, p = 0.09), and total number of nodes positive (OR 1.179, p = 0.062). Conclusions: Patients who develop very early contralateral neck disease, between completion of ipsilateral neck dissection and the initiation of radiotherapy, have a higher ratio of positive nodes to total nodes resected in the ipsilateral neck. These findings suggest that proper selection of patients for omission of treatment of the contralateral, node-negative neck should be made with this in mind, with future studies needed to document the impact on toxicity and disease outcomes from such an approach. Advances in knowledge: Pathologic risk factors in the dissected, ipsilateral neck in patients with tonsil cancer may inform the risk of contralateral neck failure. Patient selection for future, prospective efforts to examine sparing of the contralateral neck need to be based with these risk factors in mind.