Table 2.

Years since last use and duration of use of oral contraceptives in relation to breast cancer incidence by receptor status

		ER+/PR+		ER+/PR−		ER−/PR−
Use	Person-years	No. cases	IRR (95% CI)	No. cases	IRR (95% CI)	No. cases	IRR (95% CI)
Never used	128,768	102	1.00 (Ref.)*	29	1.00 (Ref.)	46	1.00 (Ref.)
Ever used	445,824	284	1.11 (0.86–1.42)	80	0.97 (0.61–1.54)	233	1.65 (1.19–2.30)
Yrs. since last use
<5	139,891	44	1.29 (0.85–1.96)	12	1.42 (0.63–3.21)	43	1.97 (1.21–3.20)
5–9	49,283	24	1.53 (0.94–2.50)	4	0.99 (0.32–3.04)	12	1.23 (0.63–2.41)
10+	256,649	216	1.07 (0.83–1.37)	64	0.94 (0.59–1.50)	178	1.64 (1.17–2.29)
Duration (yrs)
<5	250,648	150	1.03 (0.79–1.35)	43	0.91 (0.55–1.49)	139	1.67 (1.18–2.36)
5–9	110,142	64	1.09 (0.78–1.52)	25	1.31 (0.74–2.33)	44	1.37 (0.89–2.11)
10–14	63,348	52	1.45 (1.02–2.07)	9	0.82 (0.37–1.78)	35	1.83 (1.11–2.90)
15+	21,686	18	1.24 (0.74–2.09)	3	0.75 (0.22–2.54)	15	2.25 (1.23–4.11)

^*Never use of oral contraceptives is the reference category; IRRs are adjusted for age, questionnaire cycle, age at menarche, body mass index at age 18, family history of breast cancer, years of education, parity, age at first birth, age at menopause, menopausal hormone use, vigorous activity, and alcohol intake