Table 3.
Rate ratios of endometrial cancer according to baseline cigarette smoking features in the Netherlands Cohort Study, 1986–1997
| Cigarette smoking features | Categorical median | Adjusted for age | Adjusted for age, current smoking status, frequency and duration of smoking | Adjusted for all confounders | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Cases | Person-years in subcohort | RR (95% CI)a | Cases | Person-years in subcohort | RR (95% CI)b | Cases | Person-years in subcohort | RR (95% CI)c | ||
| Smoking status | ||||||||||
| Neverd | n.a. | 187 | 11,872 | 1 (ref.) | – | – | – | 169 | 10,330 | 1 (ref.) |
| Ever smokers | 93 | 8,516 | 0.70 (0.54–0.92) | – | – | – | 85 | 7,644 | 0.71 (0.53–0.95) | |
| Neverd | 187 | 11,872 | 1 (ref.) | – | – | – | 169 | 10,330 | 1 (ref.) | |
| Former smokers | n.a | 50 | 4,181 | 0.77 (0.55–1.07) | – | – | – | 47 | 3,757 | 0.83 (0.58–1.20) |
| Current smokers | n.a | 43 | 4,334 | 0.64 (0.45–0.91) | – | – | – | 38 | 3,888 | 0.59 (0.40–0.88) |
| p trend | 0.01 | 0.01 | ||||||||
| Frequency (cigarettes/day) | ||||||||||
| Neverd | 0 | 187 | 11,872 | 1 (ref.) | 187 | 11,872 | 1 (ref.) | 169 | 10,330 | 1 (ref.) |
| 0.1–9 | 4 | 38 | 3,719 | 0.65 (0.45–0.95) | 37 | 3,569 | 0.86 (0.49–1.50) | 33 | 3,223 | 1.07 (0.58–1.98) |
| 10–19 | 12 | 28 | 2,438 | 0.74 (0.48–1.14) | 27 | 2,415 | 1.02 (0.54–1.92) | 25 | 2,214 | 1.28 (0.66–2.46) |
| 20+ | 20 | 22 | 2,014 | 0.70 (0.44–1.12) | 22 | 2,014 | 1.03 (0.46–2.29) | 21 | 1,798 | 1.31 (0.56–3.03) |
| p trend | 0.04 | 0.75 | 0.43 | |||||||
| Duration (years) | ||||||||||
| Neverd | 0 | 187 | 11,872 | 1 (ref.) | 187 | 11,872 | 1 (ref.) | 169 | 10,330 | 1.0 (ref.) |
| 0.1–19 | 10.5 | 23 | 2,009 | 0.74 (0.47–1.17) | 22 | 1,991 | 0.71 (0.42–1.18) | 21 | 1,848 | 0.77 (0.43–1.39) |
| 20–39 | 30 | 52 | 4,274 | 0.79 (0.57–1.10) | 51 | 4,120 | 0.80 (0.47–1.34) | 47 | 3,690 | 0.89 (0.51–1.56) |
| 40+ | 41 | 13 | 1970 | 0.42 (0.23–0.75 | 13 | 1,887 | 0.44 (0.19–1.02) | 11 | 1,697 | 0.37 (0.15–0.90) |
| p trend | 0.00 | 0.10 | 0.13 | |||||||
| Age at first exposure (years) | ||||||||||
| Neverd | n.a | 187 | 11,872 | 1 (ref.) | 187 | 11,872 | 1 (ref.) | 169 | 10,330 | 1 (ref.) |
| <19 | 17 | 34 | 3,098 | 0.71 (0.48–1.05) | 32 | 2,947 | 0.78 (0.34–1.80) | 28 | 2,724 | 0.91 (0.37–2.23) |
| 19–24 | 20 | 21 | 2,524 | 0.53 (0.33–0.86) | 20 | 2,371 | 0.60 (0.29–1.27) | 20 | 2,102 | 0.88 (0.38–2.02) |
| 25+ | 30 | 31 | 2,691 | 0.73 (0.49–1.09) | 31 | 2,596 | 0.82 (0.47–1.46) | 28 | 2,325 | 1.00 (0.53–1.87) |
| p trend | 0.01 | 0.47 | 0.94 | |||||||
| Time since cessation (years) | ||||||||||
| Neverd | n.a | 187 | 11,872 | 1 (ref.) | 187 | 11,872 | 1 (ref.) | 169 | 10,330 | 1 (ref.) |
| 20+e | 26.5 | 20 | 1,142 | 1.11 (0.68–1.84) | 17 | 1,041 | 0.80 (0.41–1.57) | 17 | 943 | 1.12 (0.52–2.41) |
| 10–19e | 14 | 14 | 1,459 | 0.62 (0.35–1.09) | 14 | 1,416 | 0.38 (0.14–1.03) | 13 | 1,270 | 0.50 (0.17–1.45) |
| 0.1–9e | 5 | 13 | 1,392 | 0.60 (0.33–1.08) | 13 | 1,347 | 0.32 (0.10–1.06) | 12 | 1,257 | 0.50 (0.12–2.00) |
| p trend | 0.03 | 0.06 | 0.26 | |||||||
aRR = rate ratios; CI = confidence interval; n.a. = not applicable
bRRs were adjusted for age (years). In addition, frequency was adjusted for current smoking status (yes/no) and duration (years); duration was adjusted for current smoking status and frequency (cigarettes/day); age at first exposure was adjusted for current smoking status, frequency, and duration; time since cessation was adjusted for frequency and duration
cRRs were adjusted as mentioned under footnote b and additionally for body mass index (kg/m2), parity (number of children), use of oral contraceptives (ever versus never), non-occupational physical activity (low, moderate, active, very active), hypertension (yes versus no), age at first child birth (years), age at menopause (years), and alcohol consumption (gram/ day)
dNever smoked cigars, pipe, or cigarettes
eEx-smokers only