The risk of level IB nodal involvement in oropharynx cancer: Guidance for submandibular gland sparing irradiation.

PURPOSE: Xerostomia remains a common side effect of head and neck irradiation. Conflicting data exist regarding the likelihood of level IB involvement for patients with oropharyngeal squamous cell cancer (OPSCC), and data are limited on this risk in patients with human papillomavirus-positive disease. This study examined surgically treated OPSCC to determine the risk of pathologic level IB nodal involvement and to identify a cohort of patients in whom ipsilateral level IB radiation therapy may be safely omitted.

METHODS AND MATERIALS: A total of 102 submandibular nodal dissections were identified (92 ipsilateral and 10 contralateral) in 92 patients from 2010 to 2016 in those undergoing primary surgical treatment and dissection of ipsilateral level IB lymph nodes. Radiographically positive cases were excluded. Retrospective chart review was used for data collection, and the rate of pathologic level IB involvement was determined.

RESULTS: The ipsilateral level IB nodal station had negative imaging and pathologically positive nodes at rates of 4.3% in OPSCC and 5.3% in human papillomavirus-positive OPSCC. Positive node burden in the ipsilateral neck at stations other than IB appeared to correlate with the risk of pathologic positive IB (pIB+) nodes: 50% of pathologically IB-negative patients had 2 or more positive nodes versus 75% of pIB+ patients who had 4 or more positive nodes.

CONCLUSIONS: Our data indicate a low risk of pathologic level IB involvement in early-stage OPSCC. High positive node burden in stations near level IB may be associated with a higher chance of pathologic level IB involvement.