Initial Feasibility and Acute Toxicity Outcomes From a Phase 2 Trial of

purposeMETHODS AND MATERIALS: This is a planned interim initial feasibility and acute toxicity report from a phase 2, prospective, nonrandomized study, which enrolled patients with stage I-II p16+ OPSCC. All patients started definitive CRT to 70 Gy in 35 fractions, and those who met de-escalation criteria on midtreatment FDG-PET at fraction 10 completed treatment at 54 Gy in 27 fractions. We report the acute toxicity and patient-reported outcomes for 59 patients with a minimum follow-up of 3 months.

resultsThere were no statistically significant differences between baseline patient characteristics in the standard and de-escalated cohorts. There were 28 of 59 (47.5%) patients who met FDG-PET de-escalation criteria and collectively received 20% to 30% less dose to critical organs at risk known to affect toxicity. At 3 months posttreatment, patients who received de-escalated CRT lost significantly less weight (median, 5.8% vs 13.0%; P < .001), had significantly less change from baseline in penetration-aspiration scale score (median, 0 vs 1; P = .018), and had significantly fewer aspiration events on repeat swallow study (8.0% vs 33.3%, P = .037) compared with patients receiving standard CRT.

conclusionsApproximately half of patients with early-stage p16+ OPSCC are selected for de-escalation of definitive CRT using midtreatment FDG-PET biomarkers, which resulted in significantly improved rates of observed acute toxicity. Further follow-up is ongoing and will be required to determine whether this de-escalation approach preserves the favorable oncologic outcomes for patients with p16+ OPSCC before adoption.