Table 3.

Associations between ever OC use, duration of OC use, and time since last OC use and endometrial cancer risk in the Nurses’ Health Study II (1989–2017)

	Person-years	Cases	Adjusted for age and calendar period		Multivariable-adjusteda
			HR	95% CI	HR	95% CI
Use of OCs
Never use	344,113	175	1.00	(ref.)	1.00	(ref.)
Ever use	1,957,361	689	0.67	(0.56–0.79)	0.77	(0.65–0.91)
Current use	181,298	18	0.53	(0.32–0.87)	0.60	(0.36–0.99)
Past use	1,762,550	663	0.67	(0.57–0.79)	0.77	(0.65–0.92)
Duration of OC use
Never use	344,113	175	1.00	(ref.)	1.00	(ref.)
≤ 1 year	334,666	154	0.82	(0.66–1.02)	0.97	(0.77–1.20)
> 1–5 years	783,484	327	0.78	(0.64–0.93)	0.91	(0.75–1.09)
> 5–10 years	529,236	145	0.55	(0.44–0.68)	0.63	(0.50–0.79)
> 10 years	309,975	63	0.39	(0.29–0.52)	0.43	(0.32–0.58)
Continuous duration of use, in yearsb			0.94	(0.92–0.95)	0.94	(0.92–0.96)
p-trendc				< 0.0001		< 0.0001
p-trendb				< 0.0001		< 0.0001
Duration of OC use and time since last OC used
Never use	344,113	175	1.00	(ref.)	1.00	(ref.)
≤ 1 year of use	334,666	154	0.82	(0.66–1.02)	0.96	(0.77–1.20)
> 1–5 years of use and ≤ 10 years since last use	197,255	40	0.76	(0.53–1.08)	0.89	(0.63–1.27)
> 1–5 years of use and > 10 years since last use	534,797	278	0.79	(0.65–0.95)	0.91	(0.75–1.11)
> 5 years of use and ≤ 10 years since last use	324,053	43	0.37	(0.26–0.52)	0.43	(0.31–0.60)
> 5 years of use and > 10 years since last use	344,061	146	0.55	(0.44–0.69)	0.62	(0.50–0.78)

^aAdjusted for age (months), calendar period, BMI (kg/m², continuous), number of full-term pregnancies (continuous), smoking status (never/past/current), menopausal status (premenopausal/postmenopausal/perimenopausal or unknown), use of HT (never/ever), diagnosis of PCOS (yes/no), laparoscopically confirmed endometriosis (yes/no), age of menarche (years), and use of IUD/diaphragm (yes/no)

^bCalculation including ever OC users only

^cCalculation including never OC users

^dCurrent OC users were excluded from this analysis