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Purpose: The evidence for adjuvant therapy of oral cavity squamous cell carcinoma (OCSCC) in National Comprehensive Cancer Network (NCCN) guidelines is derived from patients with head and neck cancer. Here, we examined whether adjuvant therapy should be guided by a detailed analysis of pathologic risk factors in patients with pure OCSCC.Methods and Materials: Between 2004 and 2016, we retrospectively reviewed 1200 consecutive patients with OCSCC who underwent radical surgery and neck dissection in the Chang-Gung Memorial Hospital (CGMH). Patients were divided into 3 prognostic groups. High-risk patients were those with extranodal extension (ENE) and/or positive margins (ENE/margins+, n = 267). Intermediate-risk patients were further divided into 3 subgroups: (1) patients in whom adjuvant therapy was indicated according to the CGMH but not the NCCN guidelines (NCCN[-]/CGMH[+], n = 14); (2) patients in whom adjuvant therapy was indicated by the NCCN but not the CGMH guidelines (NCCN[+]/CGMH[-], n = 160); and (3) patients in whom adjuvant therapy was indicated according to both guidelines (NCCN[+]/CGMH[+], n = 411). Low-risk patients were those for whom adjuvant therapy was not suggested in light of either guideline (NCCN[-]/CGMH[-], n = 348).Results: According to NCCN guidelines, postoperative adjuvant therapy was indicated in 69.8% of the participants. However, only 57.7% of patients were in need of adjuvant therapy by CGMH guidelines. The following 5-year outcomes were observed in the NCCN(-)/CGMH(-), NCCN(-)/CGMH(+), NCCN(+)/CGMH(-), NCCN(+)/CGMH(+), and ENE/margins+ subgroups: locoregional control, 88%/70%/83%/79%/68%, P < .001 (NCCN[+]/CGMH[-] vs NCCN[+]/CGMH[+], P = .576); distant metastases, 2%/7%/2%/9%/36%, P < .001 (NCCN[+]/CGMH[-] vs NCCN[+]/CGMH[+], P = .003); disease-specific survival, 97%/86%/94%/84%/56%, P < .001 (NCCN[+]/CGMH[-] vs NCCN[+]/CGMH[+], P < .001); and overall survival, 92%/86%/87%/68%/42%, P < .001 (NCCN[+]/CGMH[-] vs NCCN[+]/CGMH[+], P < .001), respectively.Conclusions: Patients in the NCCN(+)/CGMH(-) subgroup, 28% (160/571[160 + 411]) of NCCN intermediate-risk patients, had more favorable 5-year disease-specific and overall survival (94% and 87%) than the NCCN(+)/CGMH(+) subgroup. The former are unlikely to derive clinical benefits from NCCN guidelines. The 70% adjuvant therapy rate required by NCCN guidelines after radical surgery might be too high, ultimately leaving room for improvement. [ABSTRACT FROM AUTHOR]