Table 4. Multivariable model for lung cancer risk among lifetime never–smokers.
| Factors | All females recruited | Postmenopausal females | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Lung cancer | Adenocarcinoma | Lung cancer | Adenocarcinoma | ||||||||
| Cases (N=1,454) | Model a†, HR (95% CI) | Cases (N=1,143) | Model a†, HR (95% CI) | Cases (N=1,220) | Model b‡, HR (95% CI) | Cases (N=946) | Model b‡, HR (95% CI) | ||||
| Menopause status | |||||||||||
| Natural menopause | 1,140 | Ref | 875 | Ref | |||||||
| Surgical menopause | 80 | 1.67 (1.32–2.11) | 71 | 1.83 (1.39–2.29) | |||||||
| Age at menopause, year | |||||||||||
| <45 | 75 | Ref | 65 | Ref | |||||||
| 45–49 | 364 | 0.84 (0.65–1.09) | 282 | 0.78 (0.59–1.03) | |||||||
| 50–54 | 704 | 0.92 (0.72–1.18) | 539 | 0.84 (0.65–1.10) | |||||||
| ≥55 | 77 | 0.97 (0.70–1.35) | 60 | 0.90 (0.63–1.29) | |||||||
| Age at menarche, year | |||||||||||
| <13 | 129 | Ref | 103 | Ref | 95 | Ref | 75 | Ref | |||
| 13 | 250 | 1.11 (0.90–1.37) | 191 | 1.16 (0.92–1.47) | 208 | 1.21 (0.95–1.54) | 158 | 1.17 (0.89–1.55) | |||
| 14 | 345 | 1.15 (0.93–1.40) | 259 | 1.17 (0.94–1.47) | 284 | 1.21 (0.96–1.53) | 206 | 1.13 (0.86–1.47) | |||
| 15 | 292 | 1.24 (1.01–1.53) | 240 | 1.42 (1.13–1.78) | 242 | 1.27 (1.00–1.62) | 198 | 1.34 (1.02–1.75) | |||
| ≥16 | 438 | 1.46 (1.19–1.78) | 350 | 1.58 (1.27–1.97) | 391 | 1.52 (1.21–1.90) | 309 | 1.54 (1.19–1.98) | |||
| Age at first live birth, year | |||||||||||
| Nulliparous | 26 | 1.07 (0.69–1.64) | 20 | 1.09 (0.69–1.73) | 20 | 1.16 (0.71–1.88) | 16 | 1.24 (0.72–2.12) | |||
| <25 | 443 | Ref | 326 | Ref | 392 | Ref | 284 | Ref | |||
| 25–29 | 864 | 1.29 (1.14–1.45) | 698 | 1.34 (1.18–1.53) | 714 | 1.21 (1.06–1.38) | 569 | 1.31 (1.13–1.52) | |||
| ≥30 | 121 | 1.23 (0.99–1.51) | 99 | 1.32 (1.05–1.66) | 94 | 1.13 (0.90–1.43) | 77 | 1.24 (0.95–1.61) | |||
| Duration of breastfeeding, month | |||||||||||
| 0 | 176 | Ref | 142 | Ref | 141 | Ref | 114 | Ref | |||
| 1–12 | 925 | 0.99 (0.83–1.18) | 733 | 0.94 (0.78–1.14) | 765 | 1.03 (0.85–1.25) | 596 | 1.03 (0.83–1.28) | |||
| ≥13 | 353 | 0.82 (0.67–1.00) | 268 | 0.65 (0.53–0.81) | 314 | 0.84 (0.68–1.05) | 236 | 0.84 (0.66–1.08) | |||
| Benign breast disease | |||||||||||
| No | 960 | Ref | 738 | Ref | 838 | Ref | 635 | Ref | |||
| Yes | 494 | 1.24 (1.10–1.41) | 405 | 1.30 (1.13–1.49) | 382 | 1.15 (1.01–1.33) | 311 | 1.21 (1.03–1.41) | |||
| Surgery on the reproductive system | |||||||||||
| No | 1,236 | Ref | 968 | Ref | 1,050 | Ref | 811 | Ref | |||
| Yes | 218 | 1.10 (0.94–1.27) | 175 | 1.11 (0.95–1.31) | 170 | 1.16 (0.98–1.37) | 135 | 1.16 (0.96–1.41) | |||
HR, hazard ratio; CI, confidence interval. †, Model a adjusted for age at menarche, age at first live birth, duration of breastfeeding, benign breast disease, surgery of the reproductive system, age at enrollment (continuous), education (low, medium, or high), BMI (underweight, normal, overweight or obese), smoking status (current, former or never-smoker), exposures to environmental tobacco smoke (yes or no), exposure to cooking smoke (none, little, some, or much), occupational exposures (yes or no), history of chronic respiratory disease (yes or no) and family history of lung cancer (yes or no). Province of different economic region was treated as a random variable considering within-cluster correlation. ‡, Model b adds menopause status and age at menopause to Model a.