Postoperative radiotherapy alone is as effective as postoperative chemoradiotherapy in patients with pT4aN0 gingival cancer with negative surgical margins

Background and purpose: This study compared the survival outcomes following postoperative chemoradiotherapy (CCRT) and postoperative radiotherapy (RT) alone for patients with gingival cancer with negative surgical margins and only bone invasion. Materials and methods: Of the 2579 gingival cancer cases reviewed from 2002 to 2018, 156 were enrolled in the study (CCRT: 63 patients; RT: 93 patients). The primary endpoints were the impact of adjuvant treatment (RT vs. CCRT) on overall survival (OS), locoregional recurrence-free survival (LRRFS), and distant metastasis-free survival (DMFS). Subgroup analyses were conducted based on surgical margins (<5 mm vs. ≥ 5 mm) and different adjuvant treatments (RT vs. CCRT). Results: Median follow-up time, age, and invasion depth were 88.5 months, 57 years, and 14 mm, respectively. More patients undergoing adjuvant CCRT had surgical margins < 5 mm (47.6% vs. 21.5%, p < 0.01) than those undergoing RT. No significant difference was observed in the 5-year OS, LRRFS, and DMFS of patients undergoing adjuvant RT and CCRT. Although adjuvant RT alone and CCRT provided similar local control for patients with surgical margins ≥ 5 mm, worse LRRFS trends were observed in patients with surgical margins < 5 mm (hazards ratio, 6.15, 95% confidence interval 0.92–41.13, p = 0.06). Conclusion: Postoperative RT alone may be effective for patients with gingival cancer with negative surgical margins (≥5 mm) and only bone invasion, while postoperative CCRT may result in better LRRFS than RT alone for patients with surgical margins < 5 mm.