Table 2. Cox Proportional Hazards Regression Models for the Risk of Developing Bone Metastases.

Variable	Univariable Analysis		Multivariable Analysis^a
Variable	HR (95% CI)	P Value	Adjusted HR (95% CI)	P Value
All women with early-stage breast cancer^b
Osteoporosis status	1.33 (0.89-1.97)	.16	0.87 (0.58-1.30)	.49
Age at breast cancer diagnosis	NA	NA	1.04 (1.03-1.04)	<.001
Age >55 y^c
Osteoporosis status	0.93 (0.57-1.51)	.76	0.93 (0.57-1.51)	.76
Age at breast cancer diagnosis	NA	NA	1.00 (0.98-1.02)	>.99
Age ≤55 y^d
Osteoporosis status	1.14 (0.56-2.32)	.71	0.82 (0.40-1.68)	.59
Age at breast cancer diagnosis	NA	NA	1.06 (1.04-1.08)	<.001

Abbreviations: HR, hazard ratio; NA, not applicable.

^{^a}

Models adjusted for age.

^{^b}

The exposed group included 27 of 705 patients (3.8%) with bone metastasis; the unexposed included 287 of 8399 patients (3.4%) with bone metastasis.

^{^c}

The exposed group included 19 of 429 patients (4.4%) with bone metastasis; the unexposed included 108 of 1890 patients (5.7%) with bone metastasis.

^{^d}

The exposed group included 8 of 276 patients (2.9%) with bone metastasis; the unexposed included 179 of 6509 patients (2.8%) with bone metastasis.