Adjuvant radiotherapy after curative surgery for oral cavity squamous cell carcinoma and treatment effect of timing and duration on outcome—A Taiwan Cancer Registry national database analysis

Conduct an accurate risk assessment of resected oral cavity squamous cell carcinoma (OSCC) patients by accessing a nationwide systemic investigation is pivotal to improve treatment outcomes. In this article, we tried to determine the impact of different prognostic factors for OSCC patients who received adjuvant radiotherapy (RT) after curative surgery, using Taiwan's national cancer registry database (TCR). A nationwide, large population‐based study was conducted using TCR with patients identified from 2007 to 2015. The study variables included age, gender, cancer subsites, stage, histology grade, margin and extra‐nodal extension (ENE) status, treatment type, surgery to RT interval (ORI), total RT treatment time (RTT), and RT dose. Univariate and multivariate analysis were performed to identify predictors of the variables associated with overall survival (OS), cause‐specific survival (CSS), local‐regional relapse‐free survival (LRFS), and distant metastasis‐free survival (DMFS). 8986 OSCC patients treated with surgery and adjuvant RT were analyzed. In multivariate analysis, worse outcomes were associated with males, older age, subsite in the oral tongue, advanced stage, higher histologic grade, involved margin, and positive ENE. ORI only showed an adverse trend in LRFS, when exceeding 7 weeks (P = .06). RTT >8 weeks was a significant poor predictor in OS, CSS and LRFS (P < .001). Extreme RT dose (>70 Gy or ≤50 Gy) also demonstrated an adverse impact on the outcomes. Prolonged RT treatment time and extreme RT doses were identified as significantly poor prognostic predictors in OSCC patients who received adjuvant RT after curative surgery.