Table 3. Risk Factors of Disease-Specific Mortality of Differentiated Thyroid Cancer Patients.

Variable		Univariate analysis			Multivariate analysis #1a			Multivariate analysis #2b
		HR	95% CI	P value	HR	95% CI	P value	HR	95% CI	P value
Age, yr
	≥45	9.04	5.21–15.68	<0.001	9.68	5.54–16.91	<0.001	3.44	1.44–8.20	0.005
Female sex		0.40	0.28–0.57	<0.001	0.67	0.45–0.97	0.037	0.61	0.42–0.89	0.009
Pathology
	PTC	Ref			Ref			Ref
	FTC	3.20	2.20–4.65	<0.001	2.44	1.56–3.81	<0.001	2.88	1.86–4.46	<0.001
Size of primary tumor, cm
	≤2	Ref			Ref			Ref
	2.1–4.0	3.10	2.13–4.52	<0.001	2.15	1.44–2.78	<0.001	1.82	1.21–2.74	0.004
	>4	12.46	8.33–18.62	<0.001	5.17	3.23–8.29	<0.001	4.63	2.92–7.33	<0.001
Extra-thyroidal extension
	No	Ref						Ref
	Microscopic	2.47	1.67–3.65	<0.001	2.19	1.43–3.35	<0.001	1.90	1.14–3.15	0.014
	Gross	13.73	8.46–22.31	<0.001	4.70	2.68–8.25	<0.001	2.63	1.42–4.89	0.002
LN metastasis
	N0/Nx	Ref			Ref
	N1a	0.79	0.51–1.22	0.28	0.77	0.49–1.22	0.270
	N1b	3.48	2.42–5.02	<0.001	1.81	1.18–2.78	0.007
Distant metastasis
	No	Ref			Ref
	Yes	18.04	12.00–27.10	<0.001	7.55	4.81–11.83	<0.001
TNM stage
	Stage I	Ref
	Stage II	10.60	4.82–23.32	<0.001				2.78	1.07–7.20	0.036
	Stage III	5.27	3.12–8.90	<0.001				1.58	0.67–3.70	0.290
	Stage IV	35.25	21.52–57.73	<0.001				7.21	3.05–17.06	<0.001

TNM stage was determined by the 7th American Joint Committee on Cancer TNM staging system.

HR, hazard ratio; CI, confidence interval; PTC, papillary thyroid cancer; FTC, follicular thyroid cancer; LN, lymph node; TNM, tumor node metastasis.

^aIn multivariate analysis #1, we used age at diagnosis, sex, pathology, primary tumor size, presence of extrathyroidal extension, cervical LN metastasis, and distant metastasis as possible risk factors; ^bIn multivariate analysis #2, we used age at diagnosis, sex, pathology, primary tumor size, presence of extrathyroidal extension, and TNM staging as possible risk factors.