Table 1. Correlation between Clinicopathological Factors and Median Survival Time in Patients with Stage IV Colorectal Cancer Who Had Not Undergone Nonprimary-Tumor Surgery.

Characteristic	No. of Patients	No. of Deaths	MST (months)	Log-rank	HR (95% CI)
Age at diagnosis, y, No.				<0.001
18–49	6 055	5 050	17		1 [Reference]
50–75	27 756	24 788	13		1.22 (1.18–1.25)
76–90	10 703	10 226	7		1.86 (1.80–1.93)
Sex, No.				<0.001
Female	19 258	17 328	11		1 [Reference]
Male	25 256	22 736	13		0.95 (0.93–0.97)
Race/ethnicity, No.				0.019
White	34 623	31 239	12		1 [Reference]
Black	5 887	5 377	11		1.11 (1.08–1.14)
Asian	3 329	2 863	14		0.89 (0.86–0.93)
Others and unknown	675	585	13		0.94 (0.87–1.02)
Marital status, No.				<0.001
Single	6 707	5 985	11		1 [Reference]
Married	24 361	21 724	14		0.90 (0.87–0.92)
Separated, divorced, or widowed	12 039	11 148	9		1.13 (1.09–1.16)
Unknown	1 407	1 207	12		1.00 (0.94–1.06)
Tumor grade, No.				0.017
Poorly differentiated or undifferentiated	10 639	9 850	9		1 [Reference]
Well or moderately differentiated	26 885	23 709	15		0.73 (0.71–0.75)
Unknown	6 990	6 505	7		1.17 (1.14–1.21)
Tumor location, No.				0.046
Right colon, including transverse colon	10 745	9 854	9		1 [Reference]
Left colon	16 165	14 334	14		0.77 (0.75–0.79)
Rectosigmoid or rectum	14 990	13 424	13		0.81 (0.79–0.84)
Not otherwise specified	2 614	2 452	5		1.35 (1.29–1.41)
Year of diagnosis, No.				<0.001
1988–1991	4 208	4 148	9		1 [Reference]
1992–1994	4 001	3 915	10		0.97 (0.93–1.01)
1995–1997	4 012	3 919	9		0.99 (0.95–1.03)
1998–2000	5 046	4 876	10		0.92 (0.88–0.96)
2001–2003	8 074	7 710	11		0.86 (0.83–0.89)
2004–2006	8 014	7 366	15		0.72 (0.69–0.75)
2007–2010	11 159	8 130	16		0.67 (0.65–0.70)
Primary tumor resection				<0.001
No	16 583	15 494	7		1 [Reference]
Yes	27 931	24 570	16		0.54 (0.53–0.55)

Abbreviations: CI, confidence interval; HR, hazard ratio; MST, median survival time. Survival was analyzed by using Kaplan-Meier curves and the univariate Cox regression test.