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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

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

Active cigarette smoking exposure Unexposed definition # 1a Definition # 2 Definition # 3
  cases controls ORb 95% CIb ORb 95% CIb ORb 95% CIb
Unexposed to active and secondhand smokea         
   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 smokingb         
   < 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 dayc         
   < 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-yearsc         
   < 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
  1. 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
  2. b OR, odds ratio; CI, confidence interval; adjusted for age and menopausal status
  3. c Data missing on total years smoked for 1 case, and cigs/day and pack-years for 4 cases and 2 controls