From: Smoking and risk of breast cancer in the Generations Study cohort
 | Oestrogen receptor status | All breast cancera | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Positive | Negative | Â | ||||||||||
Cases | HRb | 95% CI | P value | Cases | HRb | 95% CI | P value | Cases | HRb | 95% CI | P value | |
Age started smoking, yearsc | ||||||||||||
 Never smoked | 898 | 1.00 | Baseline |  | 167 | 1.00 | Baseline |  | 1073 | 1.00 | Baseline |  |
  < 17 | 218 | 1.25 | 1.08–1.46 | 0.0032 | 42 | 1.22 | 0.87–1.72 | 0.25 | 261 | 1.24 | 1.08–1.43 | 0.0023 |
 17–19 | 249 | 1.13 | 0.98–1.30 | 0.093 | 54 | 1.32 | 0.97–1.80 | 0.077 | 304 | 1.15 | 1.01–1.31 | 0.030 |
 20+ | 122 | 0.95 | 0.79–1.15 | 0.62 | 28 | 1.25 | 0.84–1.87 | 0.28 | 151 | 1.00 | 0.84–1.18 | 0.96 |
 Age unknown | 22 | 0.94 | 0.62–1.44 | 0.79 | 3 | 0.73 | 0.23–2.30 | 0.59 | 26 | 0.94 | 0.64–1.39 | 0.76 |
 | Trendd P = 0.17 | Trendd P = 0.74 | Trend among ever smokersd P = 0.18 | |||||||||
Trend interaction P = 0.30 |  | |||||||||||
Cigarettes per day at ages 16–24 years (among those aged ≥ 25 years at entry) | ||||||||||||
 Never smoked | 895 | 1.00 | Baseline |  | 166 | 1.00 | Baseline |  | 1069 | 1.00 | Baseline |  |
 1–4 | 77 | 1.10 | 0.87–1.39 | 0.42 | 21 | 1.65 | 1.05–2.60 | 0.032 | 99 | 1.19 | 0.97–1.46 | 0.10 |
 5–9 | 131 | 1.23 | 1.02–1.48 | 0.027 | 18 | 0.92 | 0.57–1.50 | 0.75 | 149 | 1.16 | 0.99–1.40 | 0.069 |
 10–14 | 170 | 1.11 | 0.94–1.31 | 0.22 | 31 | 1.07 | 0.73–1.57 | 0.73 | 203 | 1.10 | 0.95–1.29 | 0.21 |
 15+ | 169 | 1.13 | 0.96–1.34 | 0.14 | 42 | 1.44 | 1.02–2.03 | 0.038 | 212 | 1.18 | 1.01–1.37 | 0.034 |
 Started at age 25+ | 31 | 0.91 | 0.64–1.31 | 0.62 | 7 | 1.22 | 0.57–2.60 | 0.61 | 38 | 0.95 | 0.69–1.31 | 0.75 |
 Unknown | 31 | 0.97 | 0.68–1.39 | 0.87 | 7 | 1.32 | 0.62–2.79 | 0.47 | 38 | 1.01 | 0.73–1.40 | 0.95 |
 | Trendd P = 0.70 | Trendd P = 0.65 | Trendd P = 0.78 | |||||||||
Trend interaction P = 0.81 |  | |||||||||||
Starting smoking relative to age at menarche, years | ||||||||||||
 Never smoked | 898 | 1.00 | Baseline |  | 167 | 1.00 | Baseline |  | 1073 | 1.00 | Baseline |  |
 At or before menarche | 32 | 1.60 | 1.12–2.28 | 0.010 | 2 | 0.50 | 0.12–2.02 | 0.33 | 34 | 1.40 | 0.98–1.99 | 0.061 |
Years started after menarche | ||||||||||||
  1–4 | 217 | 1.21 | 1.04–1.41 | 0.015 | 48 | 1.38 | 1.00–1.91 | 0.049 | 266 | 1.23 | 1.07–1.41 | 0.0040 |
  5–9 | 239 | 1.09 | 0.94–1.27 | 0.23 | 54 | 1.35 | 0.99–1.84 | 0.060 | 295 | 1.13 | 0.99–1.29 | 0.071 |
  10–14 | 36 | 1.03 | 0.74–1.44 | 0.86 | 7 | 1.13 | 0.53–2.43 | 0.75 | 43 | 1.04 | 0.76–1.41 | 0.82 |
  15+ | 12 | 0.64 | 0.36–1.13 | 0.12 | 6 | 1.92 | 0.85–4.34 | 0.12 | 18 | 0.81 | 0.51–1.30 | 0.39 |
  Interval unknown | 75 | 1.02 | 0.79–1.32 | 0.88 | 10 | 0.74 | 0.38–1.41 | 0.35 | 86 | 0.99 | 0.77–1.27 | 0.92 |
 | Trendd P = 0.041 | Trendd P = 0.80 | Trendd P = 0.031 | |||||||||
Trend for interaction P = 0.42 |  | |||||||||||
Starting smoking relative to age at thelarche, years | ||||||||||||
 Never smoked | 898 | 1.00 | Baseline |  | 167 | 1.00 | Baseline |  | 1073 | 1.00 | Baseline |  |
 At or before thelarche | 16 | 1.45 | 0.88–2.39 | 0.14 | 1 | 0.45 | 0.06–3.24 | 0.43 | 17 | 1.27 | 0.79–2.06 | 0.33 |
Years started after thelarche | ||||||||||||
  1–4 | 160 | 1.17 | 0.99–1.39 | 0.075 | 31 | 1.17 | 0.79–1.72 | 0.43 | 192 | 1.17 | 1.00–1.37 | 0.056 |
  5–9 | 238 | 1.06 | 0.92–1.22 | 0.47 | 60 | 1.42 | 1.06–1.91 | 0.020 | 300 | 1.11 | 0.98–1.27 | 0.10 |
  10–14 | 37 | 0.98 | 0.70–1.36 | 0.90 | 11 | 1.60 | 0.87–2.95 | 0.13 | 48 | 1.07 | 0.80–1.43 | 0.66 |
  15+ | 18 | 0.94 | 0.59–1.50 | 0.79 | 6 | 1.83 | 0.81–4.14 | 0.14 | 24 | 1.06 | 0.71–1.59 | 0.77 |
Interval unknown | 142 | 1.22 | 1.02–1.46 | 0.031 | 18 | 0.87 | 0.53–1.42 | 0.59 | 161 | 1.17 | 0.99–1.38 | 0.074 |
 | Trendd P = 0.58 | Trendd P = 0.35 | Trend among ever smokersd P = 0.82 | |||||||||
Trend for interaction P = 0.28 |  | |||||||||||
Starting smoking relative to first childbirth, among parous (follow-up time only from first childbirth) | ||||||||||||
 Never smoked | 772 | 1.00 | Baseline |  | 148 | 1.00 | Baseline |  | 927 | 1.00 | Baseline |  |
 After first childbirth | 34 | 1.20 | 0.85–1.71 | 0.30 | 9 | 1.85 | 0.94–3.67 | 0.076 | 43 | 1.28 | 0.94–1.76 | 0.12 |
 Interval from starting smoking to first childbirth, years | ||||||||||||
  1–4 | 73 | 1.12 | 0.88–1.44 | 0.35 | 15 | 1.28 | 0.74–2.21 | 0.38 | 89 | 1.14 | 0.91–1.45 | 0.23 |
  5–9 | 177 | 1.06 | 0.90–1.25 | 0.51 | 42 | 1.35 | 0.96–1.90 | 0.089 | 220 | 1.10 | 0.94–1.28 | 0.22 |
  10–14 | 130 | 1.08 | 0.89–1.30 | 0.42 | 22 | 0.89 | 0.57–1.40 | 0.62 | 152 | 1.04 | 0.87–1.24 | 0.65 |
  15+ | 77 | 1.17 | 0.91–1.51 | 0.21 | 16 | 1.13 | 0.66–1.92 | 0.65 | 94 | 1.17 | 0.93–1.47 | 0.19 |
  Interval unknown | 22 | 1.07 | 0.70–1.64 | 0.75 | 2 | 0.54 | 0.13–2.17 | 0.38 | 25 | 1.02 | 0.69–1.52 | 0.92 |
 | Trendd P = 0.72 | Trendd P = 0.33 | Trend among ever smokersd P = 0.97 | |||||||||
Trend for interaction P = 0.27 |  |