Exploration for an Algorithm for Deintensification to Exclude the Retropharyngeal Site From Advanced Oropharyngeal Squamous Cell Carcinoma Treatment.

IMPORTANCE Understanding the drainage patterns to the retropharyngeal lymph nodes is an important consideration in oropharyngeal squamous cell carcinoma (OPSCC) because treatment of these nodes is related to increased morbidity. Prediction of these drainage patterns could not only help minimize treatment morbidity but also prevent failures in at-risk patients as deintensification trials are under way for this disease. OBJECTIVE To evaluate the prevalence of pathologic retropharyngeal adenopathy (RPA) in OPSCC relative to involvement of the oropharyngeal subsite, number of metastatic neck nodes, T classification, and N classification. DESIGN, SETTING, AND PARTICIPANTS We performed a retrospective review from January 1, 2003, through December 31, 2010, at an academic referral center of 205 previously untreated patients with pathologically confirmed, advanced-stage (III, IV) OPSCC. Data analysis was performed from January 1, 2013, through June 30, 2015. EXPOSURE Concurrent chemoradiotherapy. MAIN OUTCOMES AND MEASURES Radiologic evidence of pathologic RPA was tabulated and related to involvement of the oropharyngeal subsite, number of metastatic neck nodes, T classification, and N classification. RESULTS Of the 205 previously untreated patients (183 men; mean age, 56.1 years), pathologic RPA was identified in 37 (18.0%) of the 205 patients. Pathologic retropharyngeal lymph nodes were found in 12 (13.5%) of 89 patients with base of tongue cancers, 24 (22.0%) of 109 patients with tonsil cancers, and 1 (14.3%) of 7 patients with other oropharyngeal subsite cancers. Increasing prevalence of RPA was positively correlated with closer proximity to the posterior tonsillar pillar. A multivariable logistic regression model using the oropharyngeal subsite, involvement of the posterior tonsillar pillar, number of metastatic neck nodes, T classification, and N classification revealed that the number of metastatic neck nodes was statistically significant (odds ratio, 1.44; 95% CI, 1.20-1.71; P < .001). CONCLUSIONS AND RELEVANCE The prevalence of pathologic RPA in this cohort was 18.0%, and patients with multiple nodes had the highest risk of pathologic RPA, followed by involvement of the posterior tonsillar pillar. However, these data suggest that there is no clear algorithm that can be used for deintensification to exclude the retropharyngeal site from the treatment volume using extent of disease gathered from pretreatment imaging for patients with advanced-stage OPSCC.