Purpose: To identify adverse radiologic nodal features in cN+ TNM-8 stage I human papillomavirus-related (HPV+) oropharyngeal cancer (OPC).
Methods and materials: All patients with HPV+ cT1-T2cN1 OPC treated with definitive intensity modulated radiation therapy from 2008 to 2015 were included. Radiologically involved lymph node number (LN), radiologic extranodal extension (rENE), retropharyngeal LN (RPLN), and lower neck (level 4 or 5b) LN involvement were assessed on pre-treatment computed tomography/magnetic resonance imaging by a specialized head and neck neuroradiologist. Disease-free survival (DFS), locoregional control, and distant control were compared between those with versus without rENE. Univariable and multivariable analysis with stepwise modal selection were applied to identify prognostic factors for DFS.
Results: A total of 45 rENE+ and 234 rENE- were identified. The rENE+ cohort had a higher number of LNs per patient (median: 6 vs 2, P < .001) and was more likely to have necrotic LNs (33 [73%] vs 132 [56%], P = .046). Median follow-up was 4.8 years. Although locoregional control was high in both cohorts (93% vs 97%, P = .34), the rENE+ group had inferior 5-year distant control (78% [59-88] vs 95% [91-97], P < .001) and DFS (58% [43-77] vs 90% [86-94], P < .001). In multivariable analysis, rENE+ (HR [hazard ratio] 4.3 [2.3-8.1], P < .001], T2 (vs T1) category (HR 2.1 [1.0-4.2], P = .039), smoking pack-years (HR 1.02 [1.0-1.03], P = .013), and the addition of systemic agents (HR 0.4 [0.2-0.8], P = .005) were prognostic for DFS. RPLN was prognostic for distant metastasis (HR 3.2, P = .013) but not for DFS after adjusting for rENE.
Conclusions: Data from this contemporaneously treated cT1-T2N1 HPV+ OPC cohort suggest that the presence of rENE is an independent prognostic factor within stage I HPV+ OPC. RPLN is also associated with DM risk but not with DFS.
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