Skip to main content

Advertisement

Springer Nature is making SARS-CoV-2 and COVID-19 research free. View research | View latest news | Sign up for updates

Table 5 Relative risk of breast cancer in relation to smoking, by family history of breast cancer

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

  Family history of breast cancera
No Yes
Cases HRb 95% CI P value Cases HRb 95% CI P value
Ever previously smoked cigarettesc
 Never 819 1.00 Baseline   239 1.00 Baseline  
 Ever 554 1.07 0.96–1.20 0.22 203 1.35 1.12–1.62 0.0018
  Interaction P = 0.038
Age at start of smoking, yearsc
 Never smoker 819 1.00 Baseline   254 1.00 Baseline  
  < 20 427 1.17 1.04–1.32 0.0098 138 1.26 1.02–1.56 0.029
 20+ 96 0.82 0.67–1.02 0.076 55 1.56 1.17–2.10 0.0028
 Age unknown 16 0.75 0.46–1.23 0.26 10 1.57 0.84–2.96 0.16
  Interaction P = 0.0029
  Trendd P = 0.034   Trendd P = 0.38
Trend interaction P = 0.044
Starting smoking relative to age at menarche, years
 Never smoker 819 1.00 Baseline   254 1.00 Baseline  
 Before or < 5 years 239 1.30 1.12–1.51 0.0006 61 1.06 0.80–1.41 0.68
 5+ years 244 0.97 0.84–1.13 0.70 112 1.53 1.22–1.91 0.0002
 Interval unknown 56 0.83 0.62–1.12 0.22 30 1.51 1.02–2.24 0.041
  Interaction P = 0.0001
  Trendd P = 0.0021   Trendd P = 0.40
Trend interaction P = 0.0079
Cigarettes per day age among ever smokers, averaged over years when smokinge
 Never smoker 819 1.00 Baseline   254 1.00 Baseline  
 1–4 185 1.01 0.86–1.18 0.95 73 1.32 1.01–1.71 0.040
 5+ 210 1.28 1.09–1.49 0.0019 69 1.42 1.09–1.86 0.010
 Unknown 144 0.94 0.79–1.13 0.51 61 1.31 0.99–1.74 0.059
  Interaction P = 0.13
  Trendd P = 0.0019   Trendd P = 0.81
Trend interaction P = 0.18
Duration of smoking among ever smokers, yearsf
 Never smoker 819 1.00 Baseline   254 1.00 Baseline  
 1–9 129 0.94 0.78–1.14 0.54 48 1.20 0.88–1.64 0.24
 10+ 385 1.16 1.03–1.32 0.019 140 1.39 1.13–1.71 0.0020
 Duration unknown 25 0.76 0.51–1.13 0.17 15 1.51 0.90–2.55 0.12
  Interaction P = 0.094
  Trendd P = 0.15   Trendd P = 0.86
Trend interaction P = 0.37
Pack-years of smoking among ever smokerse
 Never smoker 819 1.00 Baseline   254 1.00 Baseline  
 1 to < 10 208 1.02 0.87–1.18 0.84 77 1.28 0.99–1.65 0.060
 10+ 187 1.30 1.11–1.53 0.0015 65 1.48 1.13–1.95 0.0051
 Unknown 144 0.93 0.78–1.12 0.46 61 1.30 0.98–1.72 0.069
  Interaction P = 0.16
  Trendd P = 0.055   Trendd P = 0.54
Trend interaction P = 0.37
  1. aFirst-degree relatives, at recruitment
  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); 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
  4. dTrend excludes never smoker and unknown groups
  5. eTime updated at the point renewed information was available from follow-up questionnaire
  6. fTime updated in yearly steps