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 4 Odds ratio (OR) among postmenopausal women according to smoking status by hormone receptor status

	Postmenopausal
	Controls	ER+/PgR+ (n = 366)						ER-/PgR- (n = 195)						P _{heterogeneity}
	Controls	Cases	OR	95% CI			p	Cases	OR	95% CI			p	P _{heterogeneity}
History of smoking
Never smoker	1829	327	1 (Reference)					172	1 (Reference)
Current	161	29	0.96	0.61	-	1.52		14	0.74	0.41	-	1.35
Past	66	10	0.67	0.33	-	1.38		9	1.25	0.59	-	2.64
Ever	227	39	0.87	0.58	-	1.29		23	0.88	0.55	-	1.44		0.95
Age at the start of smoking (years)
Never smoker	1829	327	1 (Reference)					172	1 (Reference)
26 ≤	113	14	0.69	0.38	-	1.25		10	0.87	0.44	-	1.75
20 ≤ ≤ 25	72	20	1.30	0.74	-	2.31		5	0.52	0.20	-	1.34
≤ 19	8	0	-	-	-	-		5	7.01	2.07	-	23.73
p for trend							-						0.71	-
Smoking started before first birth
Never smoker	1829	327	1 (Reference)					172	1 (Reference)
No	112	16	0.81	0.46	-	1.44		10	0.83	0.42	-	1.67
Yes	51	12	1.06	0.53	-	2.10		8	1.17	0.52	-	2.61
Uncertain	9	2	1.28	0.23	-	7.28		0	-	-	-	-
Number of cigarettes per day
Never smoker	1829	327	1 (Reference)					172	1 (Reference)
0 < ≤ 10	108	16	0.74	0.41	-	1.33		7	0.56	0.25	-	1.26
11 ≤	88	19	1.14	0.65	-	1.98		13	1.35	0.72	-	2.55
p for trend							0.99						0.79	0.82
Duration of smoking (years)
Never smoker	1829	327	1 (Reference)					172	1 (Reference)
0 < ≤ 21	48	7	0.69	0.30	-	1.62		8	1.36	0.61	-	3.03
21 <	138	25	0.93	0.57	-	1.50		12	0.78	0.41	-	1.49
p for trend							0.62						0.61	0.92
Pack-years
Never smoker	1829	327	1 (Reference)					172	1 (Reference)
0 < ≤ 13	65	9	0.67	0.31	-	1.43		6	0.76	0.31	-	1.83
13 <	118	23	1.01	0.61	-	1.67		14	1.09	0.59	-	2.00
p for trend							0.78						0.94	0.80

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 menopause (< 48, 48 ≤ < 51, 51 ≤ < 54, 54 ≤), reson of menopause (natural, others including surgery), 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).