Redefining Candidates for Deintensification in Locoregionally Advanced P16+ Oropharyngeal Cancer Based on Relative Risk

Background Randomized trials have found that patients with locoregionally advanced p16+ oropharyngeal squamous cell carcinoma (OPSCC) do not benefit from treatment deintensification, even among favorable risk groups. While various methods have been used to identify candidates for treatment deintensification, the optimal approach is unknown. Methods We conducted a multi-institutional cohort study of 444 patients with previously untreated p16+ OPSCC undergoing definitive radiotherapy with or without systemic therapy between 2009-2022. We compared two approaches for identifying candidates for deintensification: (1) favorable vs. unfavorable risk, using NRG-HN005 eligibility criteria, and (2) low vs. high relative risk for cancer events, using the HNCIG predictive classifier (“omega score”). We tested differences in outcomes and systemic therapy allocation by risk group using multivariable Cox models, competing event models, and logistic regression, and compared characteristics of hypothetical deintensification trials using the two approaches. PFS events were defined as cancer recurrence (locoregional or distant) or death from any cause. Results Median follow-up time was 52 months; 120 patients (27.0%) were favorable risk; a different 120 patients had low omega score; 28 patients (6.3%) met both criteria; 184 patients (41.4%) had discordant classification. On ordinal logistic regression, decreasing omega score was associated with a statistically significantly lower odds of receiving intensive therapy (normalized OR 0.37 per standard deviation; 95% CI: 0.24-0.57), with a greater magnitude than favorable risk group (OR 0.66; 95% CI: 0.44-0.99). Among patients receiving cisplatin and/or platinum-based induction (N=374), favorable risk was associated with significantly improved PFS (HR 0.59, 95% CI 0.36-0.99), whereas lower omega score was associated with a significantly decreased relative hazard for cancer events (RHR 0.18, 95% CI 0.070-0.46). In simulations, selecting patients with low omega scores increased the efficiency of hypothetical non-inferiority trials. Conclusions Considering patients’ relative risk for cancer events can help define optimal populations for treatment deintensification in p16+ OPSCC.