Table 2.

Univariate and multivariate analyses of clinicopathologic and treatment factors for DSS

	Univariate		Multivariate
	HR (95% CI)	p	HR (95% CI)	p
Age
Young group (ref)	1		1
Older group	1.685 (1.321–2.149)	< 0.001	1.593 (1.240–2.047)	< 0.001
Sex
Male(ref)	1		1
Female	0.695 (0.596–0.809)	< 0.001	0.910 (0.758–1.093)	0.3130
Period
1990–1999 (ref)	1		1
2000–2009	0.856 (0.737–0.994)	0.0420	0.852 (0.710–1.023)	0.0857
2010–2013	0.667 (0.546–0.813)	< 0.001	0.694 (0.56–0.861)	< 0.001
Site
Tongue (ref)	1		1
Other site of OC	1.855 (1.618–2.126)	< 0.001	1.389 (1.202–1.604)	< 0.001
Lip	0.447 (0.239–0.836)	0.0117	0.470 (0.249–0.888)	0.0201
Smoking history
Smoker (ref)	1		1
Never	1.349 (1.166–1.561)	< 0.0001	0.992 (0.817–1.203)	0.9311
Unknown	0.898 ( 0.726–1.111)	0.3211	0.951 (0.620–1.458)	0.8172
Alcohol use history
Drinker (ref)	1		1
Never	1.365 (1.164–1.602)	0.0001	1.097 (0.906–1.328)	0.3443
Unknown	0.869 (0.719–1.050)	0.1457	0.870 (0.587–1.290)	0.4899
T classification
T1(ref)	1		1
T2	1.800 (1.482–2.187)	< 0.001	1.454 (1.191–1.775)	< 0.001
T3	2.840 (2.225–3.625)	< 0.001	1.540 (1.133–2.094)	< 0.001
T4	3.590 (2.942–4.380)	< 0.001	1.727 (1.313–2.271)	< 0.001
Unknown	1.488 (0.658–3.365)	0.3399	1.065 (0.253–4.489)	0.9315
N classification
N0 (ref)	1		1
N1-3	2.480 (2.149–2.861)	< 0.001	1.684 (1.350–2.102)	< 0.001
Unknown	2.548 (1.988–3.265)	< 0.001	0.985 (0.180–5.391)	0.9865
Distant metastases
M0 (ref)	1		1
M1	5.704 (2.706–12.021)	< 0.0001	3.118 (1.453–6.688)	0.0035
Tumor stage
Stage I–II (ref)	1		1
Stage III–IV	2.613 (2.258–3.023)	< 0.001	2.425 (2.111–2.785)	< 0.001
Unknown	2.827 (2.198–3.634)	< 0.001	1.061 (0.187–6.017)	0.9466
Treatment
Surgery only (ref)	1		1
Surgery with RT/CT	1.698 (1.443–1.999)	< 0.001	1.297 (1.088–1.546)	< 0.001
RT/CT	4.606 (3.904–5.435)	< 0.001	3.156 (2.605–3.824)	< 0.001

A Cox proportional hazards model was used to analyze predictors of survival. P value < 0.01 indicates a statistically significant difference