Table 2. Prognostic factors for overall mortality.

	Unadjusted a		Cox regression, full model b		Cox regression, variable selection c
	HR (95% CI)	P d	HR (95% CI)	P d	HR (95% CI)	P d
C-stage
C-stage 0	Reference	<0.001	Reference	0.001	Reference	<0.001
C-stage I	2.80 (1.95–4.02)		1.91 (1.28–2.85)		1.98 (1.36–2.90)
Age (years)	1.08 (1.06–1.10)	<0.001	1.07 (1.05–1.09)	0.000	1.07 (1.05–1.09)	<0.001
Gender
Male	Reference	0.577	Reference	0.612	—
Female	0.91 (0.63–1.32)		0.94 (0.62–1.42)
BMI (kg m−2)	0.93 (0.89–0.97)	0.001	0.94 (0.89–0.99)	0.010	0.94 (0.89–0.98)	0.006
ASA stage
II	Reference	<0.001	Reference	0.235	—
III/IV	2.58 (1.79–3.73)		1.22 (0.77–1.95)
Cardiovascular disease
No	Reference	<0.001	Reference	0.641	—
Yes	2.27 (1.50–3.42)		1.04 (0.61–1.77)
Chronic obstructive pulmonary disease
No	Reference	0.003	Reference	0.553	—
Yes	2.21 (1.36–3.60)		1.03 (0.60–1.78)
Chronic kidney disease
No	Reference	0.002	Reference	0.106	Reference	0.049
Yes	4.04 (1.90–8.62)		2.01 (0.85–4.74)		2.28 (1.03–5.04)
AJCC stage
I	Reference	<0.001	Reference	0.006	Reference	0.004
II	1.80 (1.11–2.91)		1.36 (0.81–2.28)		1.41 (0.85–2.32)
III	2.66 (1.70–4.17)		2.12 (1.29–3.49)		2.08 (1.31–3.31)
Distance to anal verge
>10 cm	Reference	0.001	Reference	0.064	Reference	0.039
>5–10 cm	1.41 (0.85–2.33)		1.52 (0.88–2.63)		1.48 (0.88–2.49)
0–5 cm	2.38 (1.45–3.92)		1.97 (1.04–3.76)		1.93 (1.11–3.37)
Neoadjuvant therapy
No	Reference	0.199	Reference	0.671	—
Yes	0.79 (0.54–1.15)		0.98 (0.62–1.56)
Operation
Anterior resection	Reference	<0.001	Reference	0.117	Reference	0.095
Abd. perineal excision	2.57 (1.64–4.04)		1.54 (0.89–2.65)		1.55 (0.92–2.62)
Operation time (hours)	1.02 (0.90–1.17)	0.637	1.02 (0.88–1.19)	0.612	—
Resection
R0	Reference	0.027	Reference	0.023	Reference	0.005
R1	5.11 (1.51–17.3)		5.48 (1.50–20.0)		5.65 (1.59–20.1)
Adjuvant therapy
No	Reference	0.037	Reference	0.615	—
Yes	0.67 (0.45–0.99)		0.96 (0.60–1.54)

Abbreviations: AJCC=American Joint Committee on Cancer; ASA=American Society of Anesthesiologists.

Hazard ratios (HR) with 95% confidence intervals resulting from:

^aUnivariate, Cox proportional hazards regression analysis for overall mortality;

^bIndependent, full model Cox proportional hazards regression analysis for overall mortality;

^cIndependent, backward variable selection Cox proportional hazards regression analysis for overall mortality (confirmed by forward variable selection with identical results);

^dP-values from likelihood ratio tests.