Cigarette smoking and breast cancer risk in relation to joint estrogen and progesterone receptor status: a case-control study in Japan

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Table 3 Odds ratio (OR) among premenopausal women according to smoking status by hormone receptor status

	Premenopausal
	Controls	ER+/PgR+ (n = 276)						ER-/PgR- (n = 92)						P _{heterogeneity}
	Controls	Cases	OR	95% CI			p	Cases	OR	95% CI			p	P _{heterogeneity}
History of smoking
Never smoker	668	204	1 (Reference)					69	1 (Reference)
Current	220	51	0.89	0.60	-	1.32		20	0.92	0.52	-	1.64
Past	49	21	1.09	0.59	-	2.02		3	0.49	0.14	-	1.69
Ever	269	72	0.94	0.65	-	1.34		23	0.82	0.48	-	1.42		0.67
Age at the start of smoking (years)
Never smoker	668	204	1 (Reference)					69	1 (Reference)
26 ≤	42	12	1.19	0.57	-	2.47		3	0.61	0.18	-	2.12
20 ≤ ≤ 25	167	40	0.80	0.52	-	1.24		16	0.93	0.50	-	1.74
≤ 19	47	15	1.12	0.56	-	2.26		4	0.83	0.27	-	2.54
p for trend							0.65						0.68	0.92
Smoking started before first birth
Never smoker	668	204	1 (Reference)					69	1 (Reference)
No	56	12	0.75	0.36	-	1.57		3	0.43	0.12	-	1.48
Yes	136	39	0.94	0.59	-	1.50		14	0.93	0.47	-	1.81
Uncertain	14	4	0.95	0.28	-	3.23		2	1.15	0.23	-	5.63
Number of cigarettets per day
Never smoker	668	204	1 (Reference)					69	1 (Reference)
0 < ≤ 10	139	38	0.93	0.59	-	1.46		11	0.72	0.35	-	1.48
11 ≤	118	30	0.92	0.56	-	1.50		11	0.87	0.42	-	1.78
p for trend							0.68						0.53	0.75
Duration of smoking (years)
Never smoker	668	204	1 (Reference)					69	1 (Reference)
0 < ≤ 21	184	40	0.93	0.60	-	1.46		11	0.71	0.34	-	1.47
21 <	69	23	0.79	0.45	-	1.39		10	0.94	0.44	-	2.01
p for trend							0.41						0.63	0.93
Pack-years
Never smoker	668	204	1 (Reference)					69	1 (Reference)
0 < ≤ 13	165	37	0.82	0.52	-	1.29		9	0.56	0.26	-	1.21
13 <	86	26	0.98	0.58	-	1.66		11	1.06	0.51	-	2.22
p for trend							0.68						0.69	0.91

All models were adjusted by age (continuous), BMI (< 18.5, 18.5 ≤ < 25.0, 25.0 ≤ < 30.0, 30.0 ≤), occupation (professional or clerical work, industrial work or fishery, agriculture or forestry, other), physical activity (almost no, more than one hour per week), age at menarche (≤ 12, 13, 14, 15 ≤), age at first birth (≤ 24, 25 ≤ ≤ 29, 30 ≤ ≤ 50), family history of breast cancer in mother or sister (yes, no), parity number (0, 1, 2, 3 ≤), use of exogenous female hormone or oral contraceptives (yes, no), referrel status (from screening, other), year of recruitment (continuous), area of residence (Southern Miyagi prefecture, other area) and alcohol drinking (never, current or past).