Table 3.
Multivariatea rate ratios estimates and 95% confidence intervals of colorectal cancer overall, and by location among ever smokers according to various measures of smoking exposure at enrolment compared with never smokers among 68,160 women
| Colorectal cancer n = 425 | Colon cancer n = 284 | Rectum cancer n = 141 | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Cases/cohort | RR | 95% CI | Cases | RR | 95% CI | Cases | RR | 95% CI | |
| Smoking status | |||||||||
| Never | 150/24,582 | 1.0 | Ref | 97 | 1.0 | Ref | 53 | 1.0 | Ref |
| Former | 147/21,501 | 1.3 | (1.0–1.6) | 107 | 1.4 | (1.1–1.9) | 40 | 0.9 | (0.6–1.4) |
| Current | 128/22,077 | 1.2 | (0.9–1.5) | 80 | 1.1 | (0.8–1.6) | 48 | 1.2 | (0.8–1.8) |
| Ever | 275/43,578 | 1.2 | (1.0–1.5) | 187 | 1.3 | (1.0–1.7) | 88 | 1.1 | (0.7–1.5) |
| Ever smokers | |||||||||
| Smoking initiation | |||||||||
| ≥20 | 140/17,756 | 1.2 | (0.9–1.5) | 98 | 1.3 | (1.0–1.7) | 42 | 1.0 | (0.6–1.5) |
| <20 | 135/25,822 | 1.3 | (1.0–1.6) | 89 | 1.3 | (1.0–1.8) | 46 | 1.2 | (0.8–1.8) |
| p trendb | <0.05 | 0.05 | 0.5 | ||||||
| Latency (years between smoking initiation and cohort enrolment) | |||||||||
| 1–29 | 55/17,249 | 1.1 | (0.8–1.5) | 37 | 1.2 | (0.8–1.8) | 18 | 0.9 | (0.5–1.5) |
| 30–39 | 127/21,148 | 1.2 | (0.9–1.5) | 88 | 1.3 | (1.0–1.8) | 39 | 1.0 | (0.6–1.5) |
| ≥40 | 93/5,181 | 1.3 | (1.0–1.7) | 62 | 1.3 | (0.9–1.8) | 31 | 1.3 | (0.8–2.1) |
| p trendb | 0.5 | 0.9 | 0.3 | ||||||
| Number of cigarettes per day | |||||||||
| 1–9 | 165/24,927 | 1.2 | (1.0–1.5) | 114 | 1.3 | (1.0–1.7) | 51 | 1.0 | (0.7–1.5) |
| 10–14 | 81/12,900 | 1.3 | (1.0–1.7) | 53 | 1.4 | (1.0–1.9) | 28 | 1.2 | (0.8–2.0) |
| ≥15 | 29/5,751 | 1.1 | (0.7–1.7) | 20 | 1.2 | (0.7–2.0) | 9 | 0.9 | (0.4–1.9) |
| p trendb | 0.14 | 0.11 | 0.7 | ||||||
| Number of years smoked | |||||||||
| 1–19 | 78/15,157 | 1.1 | (0.8–1.5) | 55 | 1.2 | (0.9–1.7) | 23 | 0.9 | (0.5–1.5) |
| 20–29 | 66/13,592 | 1.2 | (0.9–1.6) | 47 | 1.4 | (1.0–2.0) | 19 | 0.9 | (0.5–1.6) |
| ≥30 | 131/14,829 | 1.3 | (1.0–1.6) | 85 | 1.3 | (1.0–1.8) | 46 | 1.3 | (0.8–1.9) |
| p trendb | 0.04 | 0.07 | 0.3 | ||||||
| Number of pack-years smoked | |||||||||
| 0–9 | 113/21,609 | 1.0 | (0.8–1.3) | 78 | 1.1 | (0.8–1.5) | 35 | 0.9 | (0.6–1.3) |
| 10–19 | 103/14,584 | 1.5 | (1.1–1.9) | 75 | 1.7 | (1.2–2.3) | 28 | 1.1 | (0.7–1.7) |
| ≥20 | 59/7,385 | 1.3 | (1.0–1.8) | 34 | 1.2 | (0.8–1.8) | 25 | 1.5 | (0.9–2.5) |
| p trendb | 0.008 | 0.03 | 0.13 | ||||||
| Time since quitting smoking (years) | |||||||||
| ≥20 | 52/6,777 | 1.1 | (0.8–1.5) | 36 | 1.2 | (0.8–1.7) | 16 | 0.9 | (0.5–1.6) |
| 10–19 | 46/6,122 | 1.5 | (1.1–2.1) | 24 | 1.7 | (1.2–2.6) | 5 | 1.1 | (0.6–2.1) |
| 1–9 | 49/8,602 | 1.1 | (0.8–1.7) | 33 | 1.5 | (1.0–2.4) | 13 | 0.5 | (0.2–1.3) |
| 0 (Current) | 128/22,077 | 1.2 | (1.0–1.5) | 84 | 1.2 | (0.9–1.6) | 34 | 1.2 | (0.8–1.8) |
| p trendb | 0.11 | 0.16 | 0.5 | ||||||
aAdjusted for age, menopausal status, hormonal contraceptive and postmenopausal hormonal therapy use, BMI and alcohol consumption, all at enrolment
bNever smokers included in the model