Table 3. Crude-a and multivariate-b adjusted hazard ratio (HR) estimates with 95% confidence intervals (CIs) for breast cancer among parous women according to smoking initiation in relation to first birth for ever smokers, overall, restricted to non-drinkers and by age at diagnosis, Norwegian Women and Cancer Study, 1991–2012.
|
All parous women (N=117 930) |
Non-drinkers of alcohol |
Age at diagnosis <50 years |
Age at diagnosis 50+ years |
||||||
|---|---|---|---|---|---|---|---|---|---|
| Smoking exposures | Cases (n=2877) | HRa 95% CI | HRb 95% CI | Cases (n=189) | HRb 95% CI | Cases (n=514) | HRb 95% CI | Cases (n=2363) | HRb 95% CI |
| Neverc | 352 | 1.00 (ref) | 1.00 (ref) | 84 | 1.00 (ref) | 48 | 1.00 (ref) | 304 | 1.00 (ref) |
| Ever, time of smoking initiation | |||||||||
| After first birth | 372 | 1.08 (0.93–1.25) | 1.1 (0.95–1.29) | 17 | 0.81 (0.47–1.40) | 48 | 0.97 (0.64–1.49) | 324 | 1.13 (0.96–1.33) |
| Around or <5 years before first birth | 948 | 1.16 (1.03–1.32) | 1.17 (1.03–1.33) | 44 | 1.16 (0.78–1.72) | 184 | 1.25 (0.89–1.76) | 764 | 1.16 (1.01–1.34) |
| ⩾5 years before | 1205 | 1.4 (1.24–1.58) | 1.29 (1.14–1.46) | 44 | 1.38 (0.95–2.02) | 234 | 1.48 (1.10–1.44) | 971 | 1.26 (1.11–1.45) |
| P-trendd | <0.0001 | 0.01 | 0.009 | 0.01 | 0.1 | ||||
a
Adjusted for age.
b
Adjusted for age, duration of education, hormone therapy, age at menarche, family history of breast cancer, age at first birth, number of children, hormonal contraceptive use, menopausal status, alcohol consumption when applicable and BMI all at enrolment.
c
Never, excluding active and passive, smokers as reference group.
d
Test for trend excluding never smokers.