Among patients with oral cavity squamous cell carcinoma does timing of adjuvant radiation therapy affect survival?

Background Prior studies have investigated postoperative radiation therapy (PORT) timing and its impact on head and neck squamous cell carcinoma (HNSCC) patients. However, the effect of timely initiation of PORT among the subset of oral cavity squamous cell carcinoma (OCSCC) patients has not been reported. Purpose The purpose of this study was to determine if starting PORT within 6 weeks of surgery versus 6 to 12 weeks was associated with improved survival among OCSCC patients. Study Design, Setting, Sample This retrospective cohort study reviewed data from the National Cancer Database (NCDB) from 2004 to 2019. OCSCC patients treated with curative intent surgery followed by PORT were identified. Exclusion criteria included history of prior radiation, receiving PORT >12 weeks after surgery, multiple primary malignancies, or unknown survival time. Predictor Variable The primary predictor variable was time to initiation of PORT, either within 6 weeks or at 6 to 12 weeks. Main Outcome Variable The primary outcome was overall survival (OS) defined as date of diagnosis until date of death or last follow up. Covariates Demographic data, cancer-related variables and treatment characteristics were collected. Analyses Univariate survival analyses were performed using the log rank test. A multivariable Cox proportional hazards regression analysis for overall mortality was performed using a set of demographically, clinically, and biologically pertinent predictors. Statistical significance was set at a p-value of <0.05. Results 32,743 subjects were included. The mean age was 59.9 (18-90) years. 66.2% (n=21,691) were male. Median follow up was 42.6 months (IQR 19.4-79.5). Average overall survival was 55.3 months. In the univariate survival analysis, PORT timing was associated with OS when divided into 2 week (p<0.001) and 6 week (p<0.001) intervals. After accounting for covariates, starting PORT within 6 weeks was associated with improved OS compared to 6-12 weeks (HR 1.08; 95% CI 1.01 to 1.16; p=0.037). The duration of radiation therapy did not influence OS (HR 1.00; 95% CI 1.0 to 1.0; p=0.4). Conclusion Consistent with NCCN guidelines, the findings suggest that initiating PORT within 6 weeks is associated with improved survival among OCSCC patients undergoing curative intent surgery.