Table 2 Distribution of cases and controls and age-adjusted odds ratios for breast cancer among women in the combined studies in relation to smoking status and time of active smoking initiation
From: Age of smoking initiation and risk of breast cancer in a sample of Ontario women
Cases (n = 6065*) | Controls (n = 6371*) | ||||
|---|---|---|---|---|---|
Risk Factor | No. | % | No. | % | AOR (95% CI)† |
Smoking exposure | |||||
Never active/never passive | 1270 | 24.2 | 1398 | 25.1 | 1.0 (ref) |
Passive only | 1481 | 28.2 | 1699 | 30.5 | 0.97 (0.88–1.08) |
Active only | 1143 | 21.8 | 1124 | 20.2 | 1.10 (0.98–1.23) |
Both Active and Passive | 1352 | 25.8 | 1343 | 24.1 | 1.13 (1.01–1.25) |
Age of initiation | |||||
Never active/never passive smoker | 1270 | 29.2 | 1398 | 31.7 | 1.0 (ref) |
< 12 | 44 | 1.0 | 58 | 1.3 | 0.88 (0.59–1.31) |
12 – 15 | 759 | 17.8 | 848 | 19.2 | 1.02 (0.90–1.16) |
16 – 20 | 1586 | 37.2 | 1563 | 35.4 | 1.12 (1.01–1.24) |
21 – 25 | 369 | 8.7 | 350 | 7.9 | 1.13 (0.96–1.33) |
26 + | 235 | 5.5 | 195 | 4.4 | 1.26 (1.03–1.55) |
Initiation in relation to menarche | |||||
Never active/never passive smoker | 1270 | 34.0 | 1368 | 36.0 | 1.0 (ref) |
Before menarche | 216 | 5.8 | 283 | 7.4 | 0.87 (0.71–1.05) |
Initiate ≤ 5 years from menarche | 1242 | 33.2 | 1290 | 34.0 | 1.07 (0.96–1.19) |
Initiate > 5 years from menarche | 1008 | 27.0 | 860 | 22.6 | 1.26 (1.12–1.42) |
Initiation in relation to first live birth ‡ | |||||
Never active/never passive smoker | 1087 | 34.5 | 1231 | 36.5 | 1.0 (ref) |
Before first birth: | |||||
> 5 years before | 1132 | 35.9 | 1130 | 33.6 | 1.16 (1.04–1.31) |
≤ 5 years before | 677 | 21.5 | 788 | 23.4 | 0.96 (0.84–1.09) |
After first birth | 254 | 8.1 | 219 | 6.5 | 1.24 (1.02–1.52) |