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Table 2 Relative risk of breast cancer in relation to smoking status, intensity, duration, dose, and cessation, by oestrogen receptor status

From: Smoking and risk of breast cancer in the Generations Study cohort

  Oestrogen receptor status All breast cancera
Positive Negative
Cases HRb 95% CI P value Cases HRb 95% CI P value Cases HRb 95% CI P value
Ever previously smoked cigarettesc
 Never 898 1.00 Baseline   167 1.00 Baseline   1073 1.00 Baseline  
 Ever 611 1.12 1.01–1.24 0.035 127 1.25 0.99–1.58 0.063 742 1.14 1.03–1.25 0.010
   Ever smoking by oestrogen receptor status interaction P = 0.40
Cigarettes per day, averaged over years when smokingd
 Never smoked 898 1.00 Baseline   167 1.00 Baseline   1073 1.00 Baseline  
 1–4 216 1.07 0.92–1.25 0.36 41 1.11 0.79–1.56 0.54 258 1.08 0.94–1.24 0.29
 5–9 117 1.27 1.05–1.55 0.016 17 0.97 0.59–1.59 0.89 135 1.22 1.02–1.47 0.031
 10–14 68 1.37 1.07–1.76 0.013 13 1.34 0.76–2.36 0.31 82 1.37 1.09–1.72 0.0070
 15+ 51 1.48 1.11–1.97 0.0079 11 1.61 0.87–2.97 0.13 62 1.48 1.14–1.92 0.0031
 Amount unknown 159 0.94 0.79–1.12 0.51 45 1.46 1.05–2.03 0.025 205 1.03 0.88–1.20 0.71
  Trende P = 0.023 Trende P = 0.11 Trende P = 0.0060
Trend interaction P = 0.52  
Duration of smoking, yearsf
 Never smoked 898 1.00 Baseline   167 1.00 Baseline   1073 1.00 Baseline  
 1–9 139 0.95 0.79–1.13 0.57 37 1.30 0.91–1.85 0.15 177 1.00 0.85–1.18 0.97
 10–19 187 1.22 1.04–1.43 0.015 38 1.26 0.88–1.79 0.21 225 1.21 1.05–1.41 0.009
 20–29 113 1.16 0.95–1.41 0.15 28 1.59 1.06–2.38 0.025 141 1.21 1.02–1.45 0.033
 30+ 137 1.23 1.03–1.48 0.024 20 1.07 0.67–1.71 0.78 159 1.22 1.02–1.44 0.026
 Duration unknown 35 0.97 0.69–1.36 0.86 4 0.61 0.23–1.66 0.34 40 0.93 0.68–1.28 0.66
  Trende P = 0.17 Trende P = 0.85 Trende P = 0.24
Trend interaction P = 0.44  
Pack-years of smokingd
 Never smoked 898 1.00 Baseline   167 1.00 Baseline   1073 1.00 Baseline  
 1 to < 5 156 1.13 0.95–1.34 0.15 25 0.93 0.61–1.42 0.75 182 1.10 0.94–1.29 0.25
 5 to < 10 84 1.03 0.82–1.29 0.81 19 1.21 0.75–1.94 0.44 103 1.05 0.85–1.28 0.66
 10 to < 20 114 1.25 1.03–1.53 0.027 24 1.42 0.92–2.18 0.11 138 1.27 1.06–1.52 0.010
 20+ 98 1.48 1.19–1.83 0.0003 14 1.22 0.71–2.13 0.47 114 1.45 1.19–1.77 0.0002
 Amount unknown 159 0.95 0.80–1.13 0.59 45 1.47 1.06–2.05 0.022 205 1.03 0.88–1.20 0.70
  Trende P = 0.024 Trende P = 0.16 Trende P = 0.0069
Trend interaction P = 0.66  
Current or former smokingc
 Never smoked 898 1.00 Baseline   167 1.00 Baseline   1073 1.00 Baseline  
 Currentg 73 1.14 0.89–1.45 0.30 14 1.07 0.62–1.86 0.80 87 1.12 0.89–1.39 0.34
 Former 538 1.12 1.00–1.25 0.047 113 1.27 1.00–1.62 0.50 655 1.14 1.03–1.26 0.011
   Smoking status by oestrogen receptor status interaction P = 0.58
Time since cessation, yearsf
 Never smoked 898 1.00 Baseline   167 1.00 Baseline   1073 1.00 Baseline  
 Currentg smoker 73 1.14 0.90–1.46 0.28 14 1.08 0.62–1.87 0.79 87 1.12 0.90–1.40 0.31
 1–9 100 1.25 1.01–1.54 0.040 26 1.48 0.98–2.23 0.064 127 1.28 1.06–1.55 0.009
 10–19 115 1.17 0.96–1.42 0.12 28 1.42 0.94–2.13 0.10 145 1.21 1.02–1.45 0.032
 20–29 133 1.10 0.91–1.32 0.33 20 0.94 0.59–1.51 0.81 153 1.07 0.90–1.27 0.46
 30+ 170 1.05 0.88–1.24 0.61 38 1.43 0.99–2.06 0.058 209 1.10 0.94–1.28 0.24
 Duration unknown 20 1.06 0.68–1.65 0.81 1 0.29 0.04–2.08 0.22 21 0.93 0.60–1.43 0.74
  Trende P = 0.055 Trende P = 0.85 Trende P = 0.071
Trend interaction P = 0.55  
  1. aIncludes 12 breast cancers with unknown or unmeasured oestrogen receptor status
  2. bAdjusted for attained age (Cox regression time scale); time since recruitment to cohort (0, 1–2, 3+ years); birth cohort (1908–1939, 1940–1949, 1950–1959, 1960–1969, 1970–1996); benign breast disease (yes/no); family history of breast cancer in first-degree relatives (yes/no); socio-economic score (Acorn score as trend, missing); age at menarche (trend, missing); age at first pregnancy (trend, missing); parity (trend, missing); duration of breastfeeding (trend, missing); current oral contraceptive use before menopause (yes/no); alcohol consumption (never regular, trend current drinker 1 to < 60 g/day, current drinker ≥ 60 g/day, past drinker, drinker with unknown details); physical activity [log(metabolic equivalent) trend, missing]; pre-menopausal body mass index at age 20 years (trend, missing); post-menopausal body mass index (trend, missing); menopausal hormone therapy use (never used, ex-user, current oestrogen-only user, current oestrogen plus progestogen user, current user of other types, missing); menopausal status (pre- or post-menopausal) and age at menopause (trend, missing)
  3. cTime updated through follow-up period
  4. dTime updated at the point renewed information was available from follow-up questionnaire
  5. eTrend excludes never smoker and unknown group
  6. fTime updated in yearly steps
  7. gIncludes current smokers and < 1 year immediately after stopping