Table 2. Crude-a and multivariate-b adjusted hazard ratio (HR) estimates for breast cancer with 95% confidence intervals (CIs) for different measures of smoking exposures overall and stratified by menopausal and parous status, Norwegian Women and Cancer Study, 1991–2012.
|
All women (N=130 053) |
Premenopausal (n=69 561) |
Postmenopausal (n=127 422) |
Parous (n
=117 936) |
Nulliparous (n= 12 117) |
|||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Smoking exposures | Cases (n) | HRa (95% CI) | HRb (95% CI) | Cases (n) | HRb (95% CI) | Cases (n) | HRb (95% CI) | Cases (n) | HRb (95% CI) | Cases (n) | HRb (95% CI) |
|
Smoking exposures | |||||||||||
| Neverc | 411 | 1 (ref) | 1 (ref) | 57 | 1 (ref) | 354 | 1 (ref) | 352 | 1 (ref) | 59 | 1 (ref) |
| Passive | 908 | 1.19 (1.06–1.33) | 1.18 (1.05–1.33) | 162 | 1.33 (0.98–1.81) | 746 | 1.15 (1.01–1.38) | 807 | 1.2 (1.06–1.36) | 101 | 1.15 (0.83–1.59) |
| Former | 1421 | 1.23 (1.10–1.37) | 1.2 (1.07–1.34) | 233 | 1.27 (0.95–1.71) | 1188 | 1.18 (1.04–1.34) | 1283 | 1.24 (1.10–1.40) | 138 | 1.1 (0.81–1.51) |
| Current | 1392 | 1.22 (1.10–1.36) | 1.22 (1.09–1.37) | 286 | 1.33 (0.99–1.79) | 1106 | 1.19 (1.04–1.35) | 1243 | 1.28 (1.13–1.44) | 149 | 1.11 (0.81–1.52) |
| Ever | 2813 | 1.22 (1.10–1.36) | 1.21 (1.08–1.34) | 519 | 1.3 (0.98–1.73) | 2294 | 1.18 (1.05–1.33) | 2526 | 1.26 (1.12–1.41) | 287 | 1.11 (0.83–1.48) |
|
Age at initiation (years) | |||||||||||
| 25+ | 177 | 1.08 (0.91–1.29) | 1.08 (0.91–1.30) | 14 | 0.64 (0.36–1.16) | 163 | 1.13 (0.93–1.37) | 155 | 1.11 (0.92–1.34) | 22 | 1.03 (0.63–1.69) |
| 20–24 | 786 | 1.26 (1.12–1.42) | 1.22 (1.08–1.38) | 127 | 1.36 (0.99–1.87) | 659 | 1.21 (1.05–1.38) | 692 | 1.25 (1.10–1.42) | 94 | 1.22 (0.88–1.71) |
| 15–19 | 1681 | 1.21 (1.09–1.35) | 1.21 (1.08–1.36) | 362 | 1.36 (1.02–1.83) | 1 319 | 1.16 (1.02–1.32) | 1 532 | 1.27 (1.13–1.44) | 149 | 1.03 (0.75–1.41) |
| <15 | 169 | 1.34 (1.11–1.63) | 1.31 (1.07–1.59) | 16 | 0.95 (0.52–1.74) | 153 | 1.35 (1.09–1.67) | 147 | 1.38 (1.12–1.69) | 22 | 1.25 (0.73–2.13) |
| P-trendd | 0.29 | 0.27 | 0.026 | 0.85 | 0.13 | 0.8 | |||||
|
Smoking duration | |||||||||||
| 0–10 | 562 | 1.19 (1.05–1.35) | 1.18 (1.04–1.34) | 119 | 1.3 (0.94–1.79) | 443 | 1.16 (1.00–1.34) | 518 | 1.23 (1.07–1.41) | 44 | 0.97(0.66–1.44) |
| 11–20 | 750 | 1.21 (1.07–1.37) | 1.18 (1.04–1.33) | 197 | 1.3 (0.96–1.76) | 553 | 1.14 (0.99–1.32) | 657 | 1.2 (1.05–1.37) | 93 | 1.25 (0.89–1.75) |
| 21–30 | 859 | 1.24 (1.10–1.39) | 1.22 (1.08–1.38) | 169 | 1.32 (0.96–1.80) | 690 | 1.19 (1.04–1.37) | 776 | 1.29 (1.13–1.47) | 83 | 1.06 (0.75–1.50) |
| >30 | 642 | 1.25 (1.11–1.42) | 1.26 (1.10–1.44) | 34 | 1.25 (0.78–1.98) | 608 | 1.24 (1.07–1.42) | 575 | 1.33 (1.15–1.52) | 67 | 1.09 (0.76–1.58) |
| P-trendd | 0.35 | 0.25 | 0.87 | 0.32 | 0.14 | 0.87 | |||||
|
Number of pack-yearse | |||||||||||
| 0–5 | 1008 | 1.15 (1.03–1.30) | 1.15 (1.02–1.29) | 213 | 1.29 (0.96–1.75) | 795 | 1.12 (0.98–1.28) | 929 | 1.19 (1.06–1.35) | 79 | 0.96 (0.68–1.36) |
| 6–10 | 612 | 1.3 (1.14–1.49) | 1.18 (1.04–1.34) | 134 | 1.25 (0.91–1.72) | 478 | 1.15 (0.98–1.28) | 551 | 1.22 (1.07–1.40) | 61 | 1.1 (0.77–1.59) |
| 11–15 | 519 | 1.32 (1.16–1.49) | 1.31 (1.14–1.49) | 103 | 1.42 (1.01–1.99) | 416 | 1.28 (1.10–1.49) | 462 | 1.37 (1.19–1.58) | 57 | 1.18 (0.81–1.71) |
| >15 | 674 | 1.19 (1.05–1.35) | 1.29 (1.14–1.47) | 69 | 1.28 (0.88–1.85) | 605 | 1.27 (1.10–1.46) | 584 | 1.35 (1.18–1.55) | 90 | 1.24 (0.89–1.75) |
| P-trendd | 0.004 | 0.007 | 0.79 | 0.012 | 0.008 | 0.09 | |||||
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 and BMI, all at enrolment.
c
Never-active, never-passive smokers as reference group.
d
Test for trend excluding never smokers.
e
Number of cigarettes smoked per day multiplied by number of years smoked, divided by 20.