Table 3. Multivariate Cox proportional hazard model for breast cancer-specific survival (BCSS) and overall survival (OS) in 1:1 matched propensity score matching analysis with stage IV breast cancer.

Variables	n	BCSS		OS
		HR (95% CI)	Pa	HR (95% CI)	Pa
Age (years)
20–49	1,204	Reference		Reference
50–79	3,334	1.203 (1.095–1.303)	<0.001	1.257 (1.145–1.379)	<0.001
Race
White	3,284	Reference		Reference
Black	849	1.252 (1.134–1.382)	<0.001	1.286 (1.169–1.415)	<0.001
Others	397	0.887 (0.761–1.035)	0.127	0.879 (0.751–1.021)	0.092
Unknown	8	0.179 (0.025–1.272)	0.085	0.167 (0.024–1.189)	0.074
T stage
T1 + T2	2,100	Reference		Reference
T3 + T4	2,438	1.408 (1.294–1.531)	<0.001	1.407 (1.297–1.526)	<0.001
N stage
N0 + N1	2,884	Reference		Reference
N2 + N3	1,654	1.091 (1.003–1.185)	0.042	1.098 (1.012–1.190)	0.024
Grade
I + II	1,674	Reference		Reference
III + IV	2,583	1.587 (1.436–1.753)	<0.001	1.517 (1.378–1.670)	<0.001
Unknown	281	1.279 (1.118–1.464)	<0.001	1.242 (1.090–1.414)	0.001
Molecular subtype
HR+/HER2−	2,160	Reference		Reference
HR+/HER2+	780	0.702 (0.612–0.805)	<0.001	0.714 (0.617–0.804)	<0.001
HR −/HER2+	480	0.923 (0.790–1.078)	0.311	0.936 (0.806–1.088)	0.388
TNBC	798	2.663 (2.373–2.988)	<0.001	2.603 (2.327–2.912)	<0.001
Unknown	320	1.485 (1.274–1.731)	<0.001	1.486 (1.282–1.722)	<0.001
Chemotherapy status
Yes	3,077	Reference		Reference
No/Unknown	1,461	1.554 (1.412–1.710)	<0.001	1.577 (1.438–1.729)	<0.001
Bone-only metastasis
Yes	1,548	Reference		Reference
No	2,990	1.390 (1.266–1.525)	<0.001	1.369 (1.252–1.498)	<0.001
Surgery status
No	2,269	Reference		Reference
Yes	2,269	0.542 (0.499–0.589)	<0.001	0.555 (0.512–0.601)	<0.001

Notes.

Abbreviation

HR

hazard ratio

CI

confidence interval

BCSS

breast cancer-specific survival

OS

overall survival

HR

hormone receptor

HER2

human epidermal growth factor receptor 2

TNBC

triple negative breast cancer

^aThe P value was adjusted by the multivariate Cox proportional hazard regression model.