Determining the optimal timing of adjuvant chemotherapy initiation after concurrent chemoradiotherapy in locoregionally advanced nasopharyngeal carcinoma

Background: Studies on several malignancies have suggested that the time to commencement of adjuvant chemotherapy (AC) is associated with survival outcomes. There have, however, been no relevant reports of nasopharyngeal carcinoma (NPC). Patients and methods: This clinical study examined newly diagnosed patients between April 2017 and December 2020. The primary endpoint was progression-free survival (PFS). Inverse probability of treatment weighting was used to control for confounding factors. Cox models with restricted cubic splines, Kaplan-Meier method and log-rank tests were used to evaluate the relationship between AC timing and survival. Results: A total of 551 patients were identified [median age, 45 years (interquartile range 36-52 years); 383 (69.5%) male]. Restricted cubic splines demonstrated that the timing of AC initiation had a U-shaped association with PFS. The risk of disease progression decreased within 37 days and subsequently increased. From 37 to 90 days, each additional 7-day delay conferred worse PFS of 1.32 months {hazard ratio (HR): 1.14 [95% confidence interval (CI) 1.01-1.28], P = 0.04}. The cut-off value of the receiver operating characteristic curve for initiation was 69.5 days. At a median follow-up of 48 months, the PFS was significantly better in patients initiated within 69.5 days [HR: 2.18 (95% CI 1.17-4.06), log-rank P = 0.009], with a higher 3-year rate [78.8% (95% CI 75.1% to 82.7%) versus 59.0% (95% CI 42.2% to 82.5%)] than beyond 69.5 days. Positive results were also observed in secondary endpoints. The initiation group was an independent prognostic factor [HR: 2.28 (95% CI 1.42-3.66), P < 0.001]. Conclusions: The optimal timing of AC initiation is similar to 37 days after concurrent chemoradiotherapy in patients with locoregionally advanced nasopharyngeal carcinoma. A delay beyond 69.5 days is associated with compromised survival. Efforts should be made to address the reasons for delays and ensure the timely initiation of AC.