Table 4.

Multivariate RR estimates for breast cancer with 95% CI based upon 478 cases among women who have smoked for at least 20 years compared with never smokers within two (high/low) risk levels of breast cancer risk factors, Norwegian-Swedish Cohort Study, 1991-2000

Confounding variablesCases (n = 478)Multivariate adjusted* (95% CI)P
Age group at enrollment (y)30-442531.25 (0.93-1.70)0.82
45-502251.19 (0.86-1.65)
Age at menarche (y)<131450.93 (0.63-1.36)0.08
13+3331.42 (1.08-1.85)
Menopausal statusPre2761.21 (0.91-1.61)0.74
Post1981.31 (0.92-1.88)
ParityNo651.18 (0.68-2.06)0.86
Yes4131.25 (0.98-1.58)
Age at first birth (y)§<252551.31 (0.93-1.85)0.59
25+1581.15 (0.82-1.61)
Family history of breast cancer in the mother or sistersNo4321.23 (0.97-1.55)0.82
Yes461.35 (0.65-2.79)
Hormonal contraceptive useEver3581.21 (0.93-1.56)0.76
Never1201.30 (0.86-1.96)
BMI≤23.93281.30 (0.99-1.70)0.50
>23.91501.10 (0.75-1.62)
Consumption of alcoholNondrinkers821.43 (0.87-2.33)0.50
Drinkers3961.18 (0.92-1.51)
  • * Adjusted for age at enrollment, menopausal status, number of children, age at first birth, hormonal contraceptive use, and consumption of alcohol where applicable.

  • Test for heterogeneity between strata Wald χ2 statistics.

  • Missing numbers due to equivocal menopausal status.

  • § Among parous women.