Survival impact of increasing time to IMRT initiation following induction chemotherapy in nasopharyngeal carcinoma: A propensity score-matched analysis

To explore the prognostic impact of waiting time for radiotherapy (RT) after induction chemotherapy (IC) for nasopharyngeal carcinoma (NPC). A total of 648 NPC patients receiving IC between 2009 and 2011 were included. Propensity score matching (PSM) was performed to balance the variables. Survival outcomes were compared in subgroups based on time to RT (TTR) after IC. The optimal cutoff point for TTR was 28 days. A total of 330 patients were selected by 1:2 PSM. Stratified and dichotomized TTRs were both strongly correlated with prognosis. Patients with TTR > 28 days had significantly worse 5-year LRFS, DMFS, DFS and OS than those with TTR ≤ 28 days (P < 0.05). In multivariate analysis, TTR > 28 days was an independent predictor of worse LRFS [HR=2.08; 95% CI, 1.18-3.66; P = 0.011), DMFS (HR=1.65; 95% CI, 1.04-2.62; P = 0.033), DFS (HR=1.86; 95% CI, 1.35-2.62; P < 0.001) and OS (HR=1.90; 95% CI, 1.26-2.85; P < 0.001). High-risk patients with T4 or N2-3 disease were highly susceptible to RT delay with impaired DFS and OS. In high-risk patients with TTR > 28 days, concurrent chemotherapy yielded better DMFS (70.9% vs. 52.0%, P = 0.041), DFS (52.5% vs. 34.3%, P = 0.039) and OS (70.3% vs. 53.2%, P = 0.048). Prolonged waiting is detrimental to survival in NPC, and it is strongly recommended to start RT within 28 days after IC. T4/N2-3 NPC has a higher risk of treatment failure with delayed RT. With potential protection against RT delay, concurrent chemotherapy should be performed in high-risk patients as salvage therapy.