Radiation therapy dose de-escalation compared to standard dose radiation therapy in definitive treatment of HPV-positive oropharyngeal squamous cell carcinoma.

BACKGROUND: Despite existing evidence that human papillomavirus (HPV)-positive oropharyngeal squamous cell carcinoma (OPSCC) has a favorable prognosis compared to HPV-negative OPSCC, randomized studies have yet to report the effect of de-escalating radiation therapy (RT) dose for definitive treatment. The aim of this study was to assess the effectiveness of dose de-escalated RT (DDRT) vs. standard dose RT (SDRT) in patients with HPV-positive OPSCC.

METHODS: This was an observational study using the National Cancer Database (Year 2010-2014) to identify patients who had HPV-positive OPSCC and were treated with definitive RT or chemo-RT. Patients undergoing surgery were excluded. Patients receiving ≥50 Gy, but <66 Gy were categorized as receiving DDRT. Patients receiving ≥66 Gy were categorized as receiving SDRT. Inverse probability of treatment weighting (IPTW) using propensity scores was used to balance the two groups. Kaplan-Meier analysis was used to estimate overall survival (OS). Subset analyses in patients receiving RT alone and concurrent chemo-RT were also performed. Multivariable Cox proportional hazards modeling was used to evaluate factors associated with OS.

RESULTS: 759 patients with HPV-positive OPSCC were identified: 104 received DDRT and 655 received SDRT. The median follow-up was 30.5 (2.4-81.4) months. After IPTW-adjusted analysis, there was no difference in the 3-yr OS between the two groups (82.2% vs. 79.3%; P = 0.85). In the subset of patients receiving concurrent chemoradiotherapy, IPTW-adjusted analysis also did not show a difference in the 3-yr OS between the two groups (83.1% vs. 79.6%; P = 0.83). On multivariable analysis, DDRT was not associated with an inferior OS (HR 0.88; 95% CI, 0.53-1.47; P = 0.63).

CONCLUSIONS: In this study, DDRT was not associated with an inferior OS compared to SDRT in patients with HPV-positive OPSCC. Randomized clinical trials to address DDRT in this patient population are currently ongoing.