The Role of Adjuvant Chemotherapy in Surgically Managed, p16-Positive Oropharyngeal Squamous Cell Carcinoma.

Abstract

Human papillomavirus (HPV)-related oropharyngeal squamous cell carcinoma (OPSCC) has a favorable prognosis, and p16 immunohistochemistry is a surrogate marker of high-risk HPV infection and strong prognosticator. Given this favorable prognosis, treatment de-escalation for p16-positive OPSCC is now being considered with the goal of decreasing treatment-associated morbidity without compromising tumor control. The role of adjuvant chemotherapy in this setting is becoming increasingly unclear. To compare survival between surgically managed patients with p16-positive OPSCC who received adjuvant chemoradiotherapy and patients who received adjuvant radiotherapy alone. This was a cohort study of patients with OPSCC diagnosed from June 1996 to June 2010, with follow-up through December 2014, at a single tertiary referral center. One hundred ninety-five surgically managed, p16-positive patients without a history of head and neck cancer or distant metastasis at time of diagnosis were included. Patients were dichotomized into adjuvant radiotherapy and adjuvant chemoradiotherapy groups. Overall survival was the primary outcome, and disease-free survival was the secondary outcome. Propensity-weighted multivariate Cox proportional hazards analysis was conducted to quantify the effect of adjuvant chemotherapy on survival. The study included 195 patients with p16-positive, surgically managed OPSCC. Median duration of follow-up was 87 months (interquartile range, 68-116 months). Ninety patients received adjunct chemoradiotherapy (mean age, 54.3 years), 88 patients received adjuvant radiotherapy (mean age, 56.4 years), and 17 patients received surgery alone. The 5-year overall survival rate for patients who received adjuvant chemoradiotherapy was 82% (95% CI, 73%-90%) and 84% (95% CI, 76%-91%) for patients who received adjuvant radiotherapy alone. The 5-year disease-free survival rate for patients who received adjuvant chemoradiotherapy was 79% (95% CI, 71%-88%) and 79% (95% CI, 70%-88%) for patients who received radiotherapy alone. After weighting cases by the inverse probability of receiving adjuvant chemotherapy and controlling for age, comorbidity, smoking, pathological T stage, and pathological N stage, the receipt of adjuvant chemotherapy was not significantly associated with disease-free survival (adjusted hazard ratio, 0.91; 95% CI, 0.59-1.42) but was associated with a statistically insignificant yet clinically meaningful increase in all-cause mortality (adjusted hazard ratio, 1.46; 95% CI, 0.91-2.33). Among patients with p16-positive OPSCC managed surgically with adjuvant radiotherapy, the addition of adjuvant chemotherapy provided no additional disease-free survival benefit and was associated with worse overall survival. These results should help inform future clinical trials aiming to deescalate treatment for p16-positive patients.