We queried the Taiwan Cancer Registry for non-metastatic squamous cell carcinoma of the oral cavity (including lip, tongue, gum, floor of mouth, hard palate, buccal, and retromolar area) diagnosed between 2007-2013. We selected patients who received surgery upfront but with positive margins, then proceeded to adjuvant radiotherapy or adjuvant chemoradiotherapy. We investigated the interval of surgery and initiation of radiotherapy on locoregional control, distant metastasis, cancer-specific survival, and overall survival in these patients using the log-rank test and cox proportional hazards model. 

From the initial 24142 patients identified, 607 patients matched our inclusion criteria of positive surgical margins and adjuvant radiotherapy, of which 479 had information on locoregional control and distant metastasis. Patients were divided by interval of surgery and start of radiotherapy into <4 weeks, 4-5 weeks, 5-6 weeks, 6-7 weeks, and >7 weeks. We found a significant difference in overall survival (P=0.032) and cancer-specific survival (P=0.020) between these groups. When compared to patients initiating radiotherapy within 4 weeks, the overall survival hazard ratio for intervals 4-5 weeks, 5-6 weeks, 6-7 weeks, and >7 weeks were 1.02 (0.73-1.42), 1.17 (0.85-1.63), 1.00 (0.65-1.52), and 1.57 (1.13-2.19). The cancer-specific survival hazard ratio for respective groups were 1.12 (0.78-1.62), 1.23 (0.85-1.77), 1.07 (0.66-1.68), and 1.75 (1.22-2.52). We did not find a statistically significant correlation between locoregional control or distant metastasis between these groups.

The interval between surgery and adjuvant radiotherapy negatively impacts cancer-specific survival and overall survival. When compared to prompt receipt of adjuvant radiotherapy, an interval of >7 weeks is associated with a worse cancer-specific survival and overall survival; however, patients who receive radiotherapy within 7 weeks postoperatively appears to have comparable cancer-specific survival and overall survival outcomes.