Table 3.

Multivariatea adjusted HR estimates for colon cancer with 95% CIs overall and by tumor location among women (N = 302,866) by various measures of smoking exposure at enrollment, compared with never smokers

Colon cancerProximal colon cancerDistal colon cancer
Cases (n = 1,846)Person-yearsHR (95% CI)Cases (n = 986)HR (95% CI)Cases (n = 654)HR (95% CI)
Smoking status
 Never8341,744,9441.00 (Ref)4381.00 (Ref)2951.00 (Ref)
 Former355824,9131.16 (1.02–1.31)1861.22 (1.02–1.45)1321.15 (0.94–1.41)
 Current6571,621,3431.22 (1.10–1.36)3621.37 (1.18–1.59)2271.12 (0.93–1.34)
Ptrendb<0.0001<0.00010.205
 Ever10122,446,2561.19 (1.09–1.32)5481.31 (1.15–1.49)3591.13 (0.96–1.32)
Ever smokersc
Age at smoking initiation, y
 ≥25240357,1011.19 (1.03–1.38)1331.24 (1.01–1.50)851.22 (0.96–1.57)
 20–24234588,7361.14 (0.98–1.32)1191.19 (0.96–1.46)941.19 (0.94–1.51)
 17–19173520,1731.22 (1.03–1.45)1061.60 (1.28–1.99)500.88 (0.65–1.20)
 ≤16117408,7821.48 (1.21–1.81)601.72 (1.30–2.29)401.18 (0.83–1.67)
Ptrendb<0.05<0.050.086
Number of cigarettes smoked per day
 1–9382824,1981.14 (1.00–1.28)2081.20 (1.02–1.42)1351.12 (0.91–1.37)
 10–194921,268,9801.23 (1.09–1.38)2661.37 (1.17–1.61)1801.17 (0.97–1.42)
 ≥20126337,8741.28 (1.06–1.55)681.48 (1.14–1.92)421.07 (0.76–1.48)
Ptrendb<0.0001<0.00010.177
Smoking duration, y
 1–194641,263,5281.16 (1.04–1.31)2411,22 (1.04–1.44)1731.16 (0.96–1.41)
 20–294041,089,7721.16 (1.02–1.31)2141,26 (1.06–1.50)1501.12 (0.91–1.38)
 30–397554,7481.37 (1.08–1.75)501,69 (1.25–1.28)201.06 (0.66–1.68)
 ≥405721,6501.47 (1.11–1.95)361.67 (1.17–2.38)151.18 (0.69–2.03)
Ptrendb<0.0001<0.00010.217
Number of pack-yearsd
 0–95011,270,1931.13 (1.00–1.26)2701.22 (1.05–1.44)1781.10 (0.91–1.33)
 10–19337862,0291.14 (1.00–1.30)1771.29 (1.07–1.54)1331.23 (1.00–1.52)
 ≥20155288,1471.33 (1.11–1.57)911.69 (1.34–2.12)451.08 (0.78–1.48)
Ptrendb<0.0001<0.00010.126
  • aAdjusted for age, body mass index, level of physical activity all at enrollment and duration of education.

  • bNever smokers included in the model.

  • cTotal numbers of ever smokers do not equal to the total in different smoking exposures due to missing values in different smoking exposure groups.

  • dPack-years were calculated as numbers of cigarettes smoked per day, divided by 20 and multiplied by smoking duration in years.