| Smoking duration (years) | |||||
| Never smoker | 1 to <20 | 20 to <30 | 30 to <40 | 40+ | |
| Squamous cell carcinoma: | |||||
| Cases | 7 | 1 | 4 | 34 | 76 |
| RR† | 1.0 | 5.49 (0.62 to 48.4) | 5.45 (1.36 to 21.9) | 15.73 (5.94 to 41.7) | 22.1 (8.82 to 55.2) |
| Small cell carcinoma: | |||||
| Cases | 2 | 1 | 5 | 60 | 110 |
| RR | 1.0 | 8.59 (0.73 to 101.7) | 10.29 (1.82 to 58.2) | 51.9 (11.84 to 227.3) | 77.0 (17.83 to 332.3) |
| Adenocarcinoma: | |||||
| Cases | 85 | 4 | 13 | 83 | 185 |
| RR | 1.0 | 0.83 (0.28 to 2.43) | 0.78 (0.39 to 1.56) | 2.43 (1.56 to 3.78) | 5.04 (3.35 to 7.60) |
| Large cell carcinoma: | |||||
| Cases | 11 | 7 | 19 | 23 | |
| RR | 1.0 | 1.21 (0.33 to 4.41) | 2.26 (0.77 to 6.68) | 3.57 (1.21 to 10.60) | |
| All histological types: | |||||
| Cases | 105 | 6 | 29 | 196 | 394 |
| RR | 1.0 | 1.03 (0.43 to 2.46) | 1.33 (0.81 to 2.16) | 4.08 (2.94 to 5.65) | 7.29 (5.36 to 9.92) |
*Separate regression models for each histological type, adjusted for age, cigarettes smoked per day and follow-up period.
†Reference category consists of never smokers. A total of 105 cases were confirmed among never smokers: 7 squamous cell carcinoma, 2 small cell carcinoma, 85 adenocarcinoma and 11 large cell carcinoma cases.