Table 2.
| Smoking status | Person-exams | Lung cancers | Person-years | Incidence rate per 1000 PY (95% CI) | Unadjusted hazards ratio‡ (95% CI) | P‡,§ |
|---|---|---|---|---|---|---|
| Combined cohorts | ||||||
| Never (referent) | 30 847 | 25 | 94 902 | 0.26 (0.17 to 0.39) | 1.00 | − |
| Former, pack-years | 22 873 | 120 | 74 313 | 1.61 (1.34 to 1.93) | 6.47 (4.20 to 9.96) | <.001 |
| <21.3‖ | 12 389 | 17 | 42 414 | 0.40 (0.23 to 0.64) | 1.61 (0.87 to 2.99) | .13 |
| ≥21.3 | 10 484 | 103 | 31 899 | 3.23 (2.64 to 3.92) | 12.35 (7.98 to 19.11) | <.001 |
| Current, pack-years | 22 085 | 139 | 70 489 | 1.97 (1.66 to 2.33) | 7.55 (4.94 to 11.55) | <.001 |
| <21.3 | 7967 | 2 | 28 153 | 0.07 (0.009 to 0.26)¶ | 0.28 (0.07 to 1.20)¶ | .09 |
| ≥21.3 | 14 118 | 137 | 42 336 | 3.24 (2.72 to 3.83) | 12.06 (7.98 to 18.42) | <.001 |
| Original cohort | ||||||
| Never (referent) | 20 384 | 13 | 43 107 | 0.30 (0.16 to 0.52) | 1.00 | − |
| Former, pack-years | 12 300 | 59 | 26 014 | 2.27 (1.73 to 2.93) | 7.50 (4.12 to 13.66) | <.001 |
| <21.3 | 6008 | 7 | 12 776 | 0.55 (0.22 to 1.13) | 1.81 (0.73 to 4.53) | .20 |
| ≥21.3 | 6292 | 52 | 13 238 | 3.93 (2.93 to 5.15) | 12.96 (7.07 to 23.77) | <.001 |
| Current, pack-years | 15 231 | 86 | 32 215 | 2.67 (2.14 to 3.30) | 8.86 (4.95 to 15.84) | <.001 |
| <21.3 | 5268 | 1 | 11 033 | 0.09 (0.002 to 0.50)¶ | 0.30 (0.04 to 2.31)¶ | .25 |
| ≥21.3 | 9963 | 85 | 21 181 | 4.01 (3.21 to 4.96) | 13.28 (7.43 to 23.74) | <.001 |
| Offspring cohort | ||||||
| Never (referent) | 10 463 | 12 | 51 795 | 0.23 (0.12 to 0.40) | 1.00 | − |
| Former, pack-years | 10 573 | 61 | 48 299 | 1.26 (0.97 to 1.62) | 5.36 (2.89 to 9.95) | <.001 |
| <21.3 | 6381 | 10 | 29 637 | 0.34 (0.16 to 0.62) | 1.44 (0.62 to 3.33) | .39 |
| ≥21.3 | 4192 | 51 | 18 662 | 2.73 (2.03 to 3.59) | 11.64 (6.21 to 21.82) | <.001 |
| Current, pack-years | 6854 | 53 | 38 274 | 1.38 (1.04 to 1.81) | 6.13 (3.28 to 11.47) | <.001 |
| <21.3 | 2699 | 1 | 17 120 | 0.06 (0.001 to 0.33)¶ | 0.26 (0.03 to 2.02)¶ | .20 |
| ≥21.3 | 4155 | 52 | 21 155 | 2.46 (1.84 to 3.22) | 10.66 (5.72 to 19.88) | <.001 |
Hazards ratios are from an unadjusted model with a five-level variable constructed on the basis of smoking status and cumulative pack-years. Never smokers serve as the reference group. CI = confidence interval; PY = pack-years.
All cells are time-updated; that is, as individuals begin and quit smoking, they contribute person-exams and person-time to various groups. An individual’s lung cancer diagnosis only contributes to the group he or she was in at the time of diagnosis.
Hazards ratio and P value columns include data from all five multiple imputations. Other columns are based on data in the first imputation only.
P values were derived from a two-sided χ2 test.
21.3 cumulative pack-years is the median cumulative pack-years among former smokers at the time of quitting.
Because fewer than five lung cancer events contributed to the estimation of the incidence rates and hazard ratios in these cells, these estimates should be interpreted with caution