Table 3. Relative risks of breast cancer by active and passive smoking.
| Stratified by age and region | Additionally adjusteda | Additionally and mutually adjustedb | |||
|---|---|---|---|---|---|
| Exposure | Cases | Controls | RR (95% CI) | RR (95% CI) | RR (95% CI) |
| Active smoking exposure | |||||
| Never smoker | 297 | 310 | 1.00 | 1.00 | |
| Past smoker | 156 | 144 | 1.13 (0.86–1.49) | 1.15 (0.87–1.53) | 1.00 |
| Current smoker | 186 | 186 | 1.04 (0.80–1.35) | 1.04 (0.79–1.36) | 0.90 (0.54–1.50) |
| Intensity (per 5 cigarettes per day) | |||||
| Ever smoker | 342 | 330 | 1.02 (0.91–1.13) | 1.00 (0.89–1.12) | 1.00 (0.88–1.12) |
| Duration (per 5 years smoked) | |||||
| Ever smoker | 342 | 330 | 1.02 (0.93–1.12) | 1.00 (0.91–1.11) | 1.02 (0.86–1.22) |
| Age started smoking (per 5 years) | |||||
| Ever smoker | 342 | 330 | 0.97 (0.80–1.19) | 0.97 (0.79–1.19) | 0.99 (0.76–1.28) |
| Active and passive exposure | |||||
| Never smoker, no passive exposure | 175 | 175 | 1.00 | 1.00 | |
| Never smoker, passive exposure | 122 | 135 | 0.90 (0.65–1.25) | 0.89 (0.64–1.25) | |
| Past smoker, no passive exposure | 58 | 52 | 1.12 (0.73–1.72) | 1.12 (0.72–1.73) | |
| Past smoker, passive exposure | 98 | 92 | 1.06 (0.75–1.51) | 1.09 (0.75–1.56) | |
| Current smoker, no passive exposure | 44 | 38 | 1.15 (0.71–1.87) | 1.19 (0.72–1.95) | |
| Current smoker, passive exposure | 142 | 148 | 0.96 (0.70–1.31) | 0.93 (0.67–1.30) | |
| Number of years of exposure to passive smoking at home | |||||
| Never smoker, 0 years | 175 | 175 | 1.00 | 1.00 | |
| Never smoker, 1–10 years | 56 | 55 | 1.02 (0.66–1.56) | 0.99 (0.64–1.53) | |
| Never smoker, 11+ years | 66 | 80 | 0.83 (0.56–1.22) | 0.84 (0.56–1.25) | |
| P-valuec=0.31 | |||||
| Past smoker, 0 years | 58 | 52 | 1.12 (0.73–1.72) | 1.12 (0.72–1.73) | |
| Past smoker, 1–10 years | 42 | 38 | 1.10 (0.68–1.79) | 1.12 (0.68–1.85) | |
| Past smoker, 11+ years | 56 | 54 | 1.04 (0.68–1.59) | 1.06 (0.68–1.66) | |
| P-valuec=0.71 | |||||
| Current smoker, 0 years | 44 | 38 | 1.15 (0.71–1.87) | 1.19 (0.72–1.96) | |
| Current smoker, 1–10 years | 31 | 44 | 0.71 (0.43–1.17) | 0.66 (0.39–1.10) | |
| Current smoker, 11+ years | 111 | 104 | 1.07 (0.76–1.50) | 1.06 (0.74–1.53) | |
| P-valuec=0.58 | |||||
a
Additionally adjusted for socioeconomic status, alcohol consumption, BMI, parity and age at first giving birth, use of oral contraceptives, family history of breast cancer, age at menarche, menopausal status.
b
Adjustments as for (a), but with mutual adjustment for all active smoking-related variables among the ever smokers.
c
P-value for linear trend test of increasing duration of passive smoking exposure.