Decrease in treatment intensity predicts worse outcome in patients with locally advanced head and neck squamous cell carcinoma undergoing radiochemotherapy.

PURPOSE: Radiochemotherapy (RCT) is an effective standard therapy for locally advanced head and neck squamous cell carcinoma (LA-HNSCC). Nonetheless, toxicity is common, with patients often requiring dose modifications. METHODS: To investigate associations of RCT toxicities according to CTCAE version 5.0 and subsequent therapy modifications with short- and long-term treatment outcomes, we studied all 193 patients with HNSCC who received RCT (70 Gy + platinum agent) at an academic center between 03/2010 and 04/2018. RESULTS: During RCT, 77 (41%, 95% CI 34-49) patients developed at least one ≥ grade 3 toxicity, including seven grade 4 and 3 fatal grade 5 toxicities. The most frequent any-grade toxicities were xerostomia (n = 187), stomatitis (n = 181), dermatitis (n = 174), and leucopenia (n = 98). Eleven patients (6%) had their radiotherapy schedule modified (mean radiotherapy dose reduction = 12 Gy), and 120 patients (64%) had chemotherapy modifications (permanent discontinuation: n = 67, pause: n = 34, dose reduction: n = 7, change to other chemotherapy: n = 10). Objective response rates to RCT were 55% and 88% in patients with and without radiotherapy modifications (p = 0.003), and 84% and 88% in patients with and without chemotherapy modifications (p = 0.468), respectively. Five-year progression-free survival estimates were 20% and 50% in patients with and without radiotherapy modifications (p = < 0.001), and 53% and 40% in patients with and without chemotherapy modifications (p = 0.88), respectively. CONCLUSIONS: Reductions of radiotherapy dose were associated with impaired long-term outcomes, whereas reductions in chemotherapy intensity were not. This suggests that toxicities during RCT should be primarily managed by modifying chemotherapy rather than radiotherapy.