Table 4.

Multivariatea adjusted HR estimates for colon cancer with 95% CIs overall and by tumor location among men (299,376) by various measures of smoking exposure at enrollment, compared with never smokers

Colon cancerProximal colon cancerDistal colon cancer
Cases (N = 2,152)Person-yearsHR (95% CI)Cases (n = 1,048)HR (95%CI)Cases (n = 866)HR (95% CI)
Smoking status
 Never5341,369,6911.00 (Ref)2671.00 (Ref)2171.00 (Ref)
 Former7441,138,8811.14 (1.02–1.27)3501.06 (0.90–1.24)3231.24 (1.03–1.47)
 Current8741,913,4771.03 (0.92–1.15)4311.02 (0.86–1.19)3260.95 (0.79–1.13)
Ptrendb0.7890.9020.368
 Ever1,6183,052,3581.08 (0.97–1.19)7811.03 (0.90–1.19)6491.08 (0.92–1.26)
Ever smokersc
Age (years) at smoking initiation
 ≥25184268,6001.01 (0.85–1.20)900.99 (0.77–1.25)751.04 (0.80–1.36)
 20–24303592,4801.08 (0.94–1.25)1441.03 (0.83–1.25)1151.04 (0.82–1.30)
 17–19311655,0951.11 (0.97–1.28)1571.12 (0.92–1.38)1161.04 (0.82–1.30)
 ≤16263639,2431.15 (0.99–1.34)1281.13 (0.91–1.40)1011.10 (0.86–1.40)
Ptrendb0.5770.9840.795
Number of cigarettes smoked per day
 1–9359604,4210.99 (0.86–1.13)1680.91 (0.75–1.11)1471.02 (0.82–1.26)
 10–197601,526,8041.09 (0.97–1.22)3731.06 (0.90–1.24)2931.04 (0.87–1.25)
 ≥20415832,8451.16 (0.97–1.28)1911.08 (0.90–1.30)1821.25 (01.02–1.53)
Ptrendb<0.050.232<0.05
Smoking duration, y
 1–194951,250,2221.06 (0.93–1.20)2290.99 (0.83–1.19)2161.12 (0.93–1.35)
 20–296611,471,5261.06 (0.94–1.20)3221.04 (0.88–1.23)2571.02 (0.85–1.22)
 30–39278241,3851.09 (0.94–1.27)1341.03 (0.83–1.28)1101.10 (0.87–1.40)
 ≥4015958,1331.29 (1.05–1.59)801.16 (0.87–1.55)621.40 (1.00–1.94)
Ptrendb<0.050.3560.219
Number of pack-yearsd
 0–9364943,7961.08 (0.94–1.23)1771.06 (0.87–1.28)1491.07 (0.87–1.32)
 10–194451,014,3051.10 (0.97–1.25)2221.10 (0.92–1.32)1641.00 (0.80–1.22)
 ≥20369647,1001.14 (0.99–1.31)1881.16 (0.96–1.41)1401.06 (0.85–1.32)
Ptrendb<0.050.1100.771
  • 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.