Table 2.

Oral contraceptive use and breast cancer risk in never, past and current oral contraceptive users, Nurses’ Health Study II.

	Cases (n=1344)	Person-years	Age-adjusted RR	Multivariate RR**
		(1,246,967)	95 percent CI	95 percent CI
Never	162	176,581	1.0(ref)	1.0(ref)
Past	1084	952,266	1.10(0.94–1.30)	1.12(0.95–1.33)
Current	98	118,120	1.36(1.06–1.76)	1.33(1.03–1.73)
> 0–8 years*	34	55,333	1.17(0.80–1.70)	1.16(0.80–1.69)
≥8 years*	57	57,899	1.47(1.08–1.99)	1.42(1.05–1.94)

^*Seven cases who were current users and 4,888 person-years among current users were missing duration of use.

^**Multivariate models control for: age (in months), follow-up cycle, body mass index (in kg/m²), family history of breast cancer (mother, sister, maternal grandmother, paternal grandmother), menopausal status, history of benign breast disease, age at menarche, history of irregular menstrual periods, current pregnancy, parity, age at first birth, duration of breastfeeding, cigarette smoking, animal fat intake, alcohol consumption and history of ovulatory infertility.