Table 3.

Joint relation of years since last use and duration of use to breast cancer incidence by receptor status

Use			ER+/PR+		ER+/PR−		ER−/PR−
Yrs. since last use	Duration (yrs)	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.)
<5	<5	54,784	10	0.89 (0.45–1.77)	5	1.77 (0.63–4.99)	12	1.54 (0.78–3.05)
	5–9	42,284	10	1.19 (0.59–2.40)	4	1.92 (0.60–6.19)	9	1.58 (0.73–3.42)
	10+	42,824	24	1.66 (1.01–2.74)	3	0.84 (0.23–13.03)	22	2.52 (1.43–4.45)
5–9	<5	24,427	12	2.13 (1.13–4.03)	1	0.72 (0.09–5.50)	4	1.03 (0.36–2.94)
	5–9	12,574	4	1.03 (0.37–2.89)	0	-	3	1.15 (0.35–3.80)
	10+	12,283	8	1.31 (0.62–2.77)	3	1.85 (0.53–6.47)	32	1.50 (0.58–3.86)
10+	<5	171,437	128	1.00 (0.76–1.32)	37	0.86 (0.52–1.44)	123	1.72 (1.21–2.44)
	5–9	55,285	50	1.10 (0.77–1.57)	21	1.35 (0.75–2.46)	32	1.35 (0.85–2.15)
	10+	29,927	38	1.33 (0.90–1.95)	6	0.64 (0.26–1.58)	23	1.69 (1.01–2.83)

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