Table 2.

Relative Risk of Endometrial Cancer Comparing Oral Bisphosphonate Users to Nonusers, Women's Health Initiative (1993 to 2010)

Oral Bisphosphonate Use*	Person-Years at Risk†	No. of Endometrial Cancer Events	Age-Adjusted Analysis			Multivariable-Adjusted Analysis
			HR‡	95% CI	P	HR‡§	95% CI	P
Any use
No	871,495	1,070	1.00		.01	1.00		.05
Yes	68,602	53	0.76	0.61 to 0.94		0.80	0.64 to 1.00
Type
Alendronate sodium	63,297	47	0.72	0.57 to 0.90	.005	0.77	0.61 to 0.98	.03
Risedronate sodium	3,349	5	1.33	0.73 to 2.42	.34	1.44	0.77 to 2.70	.25
Other‖	1,956	1	0.37	0.05 to 2.59	.31	0.40	0.06 to 2.82	.36
Duration of use, years
< 1	22,101	17	0.73	0.50 to 1.08	.11	0.85	0.57 to 1.25	.40
1 to 3	27,817	19	0.75	0.54 to 1.05	.09	0.81	0.58 to 1.15	.24
≥ 3	18,684	17	0.77	0.53 to 1.11	.16	0.76	0.51 to 1.13	.17

Abbreviations: HR, hazard ratio; WHI-CT, Women's Health Initiative clinical trials; WHI-OS, Women's Health Initiative observational study.

^*Users reported at least 2 weeks of use; nonusers include never-users and those who used for < 2 weeks. Baseline oral bisphosphonate use was updated at years 1, 3, and 6 for women in WHI-CT and at year 3 for women in WHI-OS.

^†Median follow-up time of 12.5 years.

^‡Baseline hazard stratified by Women's Health Initiative study component.

^§Adjusted for age, 5-year hip fracture probability, body mass index, race, education, smoking status, estrogen-only use, estrogen-progestin use, oral contraceptive use, parity, and mammography, all measured at baseline.

^‖Other includes etidronate disodium and tiludronate disodium.