Case-control study of tobacco smoke exposure and breast cancer risk in Delaware

BMC Cancer

Table 4 Active smoking and breast cancer among cases and controls from Delaware, using women never exposed to active or secondhand smoking as the reference group

Active cigarette smoking exposure	Unexposed definition # 1^a				Definition # 2		Definition # 3
	cases	controls	OR^b	95% CI^b	OR^b	95% CI^b	OR^b	95% CI^b
Unexposed to active and secondhand smoke^a
Definition # 1	13	14	1.00	reference
Definition # 2	30	37			1.00	reference
Definition # 3	41	46					1.00	reference
Ever active smoker	163	150	1.21	0.55–2.66	1.33	0.77–2.27	1.23	0.76–1.98
Years of smoking^b
< 20	50	59	0.98	0.42–2.31	1.10	0.59–2.05	1.03	0.58–1.82
20–39	70	58	1.31	0.57–3.02	1.45	0.80–2.63	1.35	0.77–2.36
≥ 40	42	33	1.35	0.55–3.32	1.48	0.74–2.96	1.31	0.69–2.47
Cigarettes per day^c
< 10	58	49	1.31	0.56–3.08	1.45	0.78–2.71	1.33	0.75–2.35
10–19	67	58	1.30	0.56–3.00	1.44	0.79–2.63	1.33	0.76–2.32
≥ 20	34	41	0.90	0.37–2.18	0.99	0.51–1.94	0.91	0.49–1.69
Pack-years^c
< 10	56	54	1.20	0.51–2.81	1.34	0.72–2.48	1.25	0.70–2.21
10–29	65	55	1.30	0.56–3.01	1.43	0.78–2.63	1.32	0.75–2.31
≥ 30	38	39	1.03	0.43–2.49	1.13	0.58–2.20	1.02	0.55–1.89
Any exposure before age 18	109	106	1.13	0.51–2.52	1.27	0.73–2.21	1.18	0.71–1.95
Any exposure before first live birth	120	127	1.06	0.48–2.35	1.18	0.68–2.04	1.08	0.66–1.76

^a Women unexposed to secondhand smoke were defined as follows: Definition #1: Zero years lifetime residential and occupational exposure; Definition #2: ≤ 10 years lifetime residential exposure, ≤ 10 years of moderate-level occupational exposure and ≤ 10 years heavy-level occupational exposure; Definition #3: Zero years of residential exposure before age 18
^b OR, odds ratio; CI, confidence interval; adjusted for age and menopausal status
^c Data missing on total years smoked for 1 case, and cigs/day and pack-years for 4 cases and 2 controls

ISSN: 1471-2407