Positive margin and advanced depth of invasion as the indicators for assessing the necessity of adjuvant chemoradiotherapy in early-stage oral cavity squamous cell carcinoma

e18052 Background: Adjuvant therapy was indicated for patients with a high risk of disease progression after curative therapy, and RTOC 9501/EORTC 22931 were the landmark studies for assessing the necessity of adjuvant therapy in oral cavity squamous cell carcinoma (OCSCC). However, the role of adjuvant therapy in early-staging OCSCC, which was redefined by the 8th edition American Joint Committee on Cancer (AJCC) staging system, was unknown. Methods: A total of 485 early-staging OCSCC patients (pT1-2N0) diagnosed between Jan 2010 and Dec 2019 were retrospectively enrolled. All of them were newly diagnosed and reevaluated to meet the criteria of the 8th edition AJCC staging system. Adjuvant therapy was discussed and concluded in the combined conference of the head and neck multidisciplinary team at Chung Shan Medical University Hospital. And the enrolled patients were divided into the groups with or without adjuvant therapy. The effectiveness of adjuvant therapy and prognostic factor for locoregional recurrence-free survival (LRFS) were analyzed. Results: Nearly one-sixth (16.1%, 78/485) of the enrolled patients received adjuvant therapy. The patients with adjuvant therapy were worse in pathologic T staging ( P < 0.001), histologic grade ( P < 0.001), and pathologic features (depth of invasion [DOI] > 4mm, P < 0.001; perineural invasion, P < 0.001) than those without. Positive margin and advanced DOI ( > 4mm) were the independent factors for LRFS. Adjuvant therapy did not improve LRFS that the 3-year LRFS of the patients with or without adjuvant therapy were 79.7% and 81.5%, respectively ( P = 0.718)(hazard ratio [HR], 95% confidence interval [CI]: 1.10 [0.67-1.80]). However, adjuvant chemoradiotherapy (CRT) indeed prolonged LRFS in some subgroups, such as those with positive margin or advanced DOI (the subgroup with positive margin, 3-year LRFS of those with or without adjuvant therapy, 100% and 58.8%, HR[95% CI]: 0.04[0.00-267.330]; the subgroup with advanced DOI, 3-year LRFS, 83.3% and 73.1%, HR[95% CI]: 0.48[0.16-2.01]). In addition to positive margin, advanced DOI was the most critical correlation coefficient factor among the pathologic features, including pathologic T staging, perineural invasion, lymphovascular invasion, poorly differentiated, and close margin. For the patients eligible for evaluation, forty percent (40.1%, 180/439) of the patients were diagnosed with positive margins or advanced DOI and these patients might be considered to receive adjuvant CRT in the future. Conclusions: Positive margin and DOI were the most important indicators to evaluate the necessity of adjuvant CRT in early-staging OCSCC. Future warranted studies were needed.