The impact of interval between surgery and postoperative radiotherapy in major salivary gland carcinoma

Background: Radiotherapy following primary operation is strongly recommended for salivary gland carcinomas (SGCs) with adverse features. The interval between surgery and the initiation of radiotherapy (SRT) varied and a prolonged SRT may cause failure of cancer treatment. However, the association of SRT with survival is unclear in major SGCs. Methods: This retrospective study included a total of 346 patients who underwent radiotherapy after the primary operation from Fudan University Shanghai Cancer Center from 2005 to 2020. The best cutoff value of the SRT was determined by the maximum log-rank statistic method. The primary endpoint of the study was overall survival (OS). Correlations between variables and OS were conducted by the univariable analysis using the Log-rank method, and a multivariate Cox proportional hazards regression was performed to identify the independent prognostic factors associated with OS. The estimated survival rates were captured using the Kaplan-Meier method. Results: With a median follow-up time of 70.31 months, the estimated 5-year OS, LRFS, and DMFS were 83.3%, 80.1%, and 75.9%, respectively. The cutoff value for SRT was 8.5 weeks, while age, T stage, N stage, perineural invasion (PNI), pathological aggression, chemotherapy, and SRT were associated with OS in the univariable analysis. The Cox regression analysis demonstrated that older age (P < 0.001), T3-4 tumors (P = 0.007), positive N stage (P < 0.001), pathological aggression (P = 0.014), and longer SRT (P = 0.009) were independent prognostic factors for major SGCs. Using the stratification model, we observed that delay in the SRT was associated with worse OS (P = 0.006) in the high-risk group, whereas no significant difference was observed in the low-risk subgroup (P = 0.61). Conclusions: The delay in the initiation of postoperative radiotherapy may be a prognostic factor for patients with major SGCs. It was suggested that radiotherapy should be delivered within 8.5 weeks following the operation, especially for patients with ≥2 risk factors, including older age, high pathological aggression, T3-4 tumors, and positive N stage.