Table 1. Baseline characteristics of participants by lung cancer status.
| Variable | Total (N=553,434) | No lung cancer (N=551,905) | Lung cancer (N=1,529) | P value |
|---|---|---|---|---|
| Age at enrollment, year | ||||
| Mean ± SD | 55.76±8.64 | 55.75 ±8.64 | 59.72 ±7.48 | <0.0001 |
| Age, years, No (%†) | ||||
| 40–44 | 65,069 (11.76) | 65,019 (11.78) | 50 (3.27) | <0.0001 |
| 45–49 | 90,175 (16.29) | 90,054 (16.32) | 121 (7.91) | |
| 50–54 | 100,597 (18.18) | 100,374 (18.19) | 223 (14.58) | |
| 55–59 | 92,424 (16.70) | 92,157 (16.70) | 267 (17.46) | |
| 60–64 | 98,608 (17.82) | 98,217 (17.80) | 391 (25.57) | |
| 65–69 | 79,537 (14.37) | 79,152 (14.34) | 385 (25.18) | |
| 70–74 | 27,024 (4.88) | 26,932 (4.88) | 92 (6.02) | |
| Education, No (%†) | ||||
| Low | 111,671 (20.18) | 111,306 (20.17) | 365 (23.87) | 0.0005 |
| Medium | 360,648 (65.17) | 359,717 (65.18) | 931 (60.89) | |
| High | 81,115 (14.66) | 80,882 (14.66) | 233 (15.24) | |
| Marital status, No (%†) | ||||
| Married | 516,099 (93.25) | 514,686 (93.26) | 1,413 (92.41) | 0.1894 |
| Other | 37,335 (6.75) | 37,219 (6.74) | 116 (7.59) | |
| Economic region, No (%†) | ||||
| Developed areas | 192,562 (34.79) | 192,056 (34.80) | 506 (33.09) | 0.1621 |
| Developing areas | 360,872 (65.21) | 359,849 (65.20) | 1,023 (66.91) | |
| Smoking status, No (%†) | ||||
| Never | 529,823 (95.73) | 528,369 (95.74) | 1,454 (95.09) | 0.4576 |
| Current | 19,986 (3.61) | 19,922 (3.61) | 64 (4.19) | |
| Former | 3,625 (0.66) | 3,614 (0.65) | 11 (0.72) | |
| Environmental tobacco smoke, No (%†) | ||||
| No | 344,791 (62.30) | 343,891 (62.31) | 900 (58.86) | 0.0055 |
| Yes | 208,643 (37.70) | 208,014 (37.69) | 629 (41.14) | |
| Exposure to cooking smoke, No (%†) | ||||
| None | 66,836 (12.08) | 66,668 (12.08) | 168 (10.99) | 0.6072 |
| Little | 397,183 (71.77) | 396,069 (71.76) | 1,114 (72.86) | |
| Some | 71,578 (12.93) | 71,382 (12.93) | 196 (12.82) | |
| Much | 17,837 (3.22) | 17,786 (3.22) | 51 (3.34) | |
| Occupational exposure, No (%†) | ||||
| No | 463,002 (83.66) | 461,738 (83.66) | 1,264 (82.67) | 0.2937 |
| Yes | 90,432 (16.34) | 90,167 (16.34) | 265 (17.33) | |
| BMI‡, No (%†) | ||||
| Underweight | 12,083 (2.18) | 12,047 (2.18) | 36 (2.35) | 0. 7604 |
| Normal | 303,311 (54.81) | 302,490 (54.81) | 821 (53.70) | |
| Overweight | 190,799 (34.48) | 190,266 (34.47) | 533 (34.86) | |
| Obese | 47,241 (8.54) | 47,102 (8.53) | 139 (9.09) | |
| Family history of lung cancer, No (%†) | ||||
| No | 488,776 (88.32) | 487,518 (88.33) | 1,258 (82.28) | <0.0001 |
| Yes | 64,658 (11.68) | 64,387 (11.67) | 271 (17.72) | |
| History of chronic respiratory diseases, No (%†) | ||||
| No | 440,291 (79.56) | 439,164 (79.57) | 1,127 (73.71) | <0.0001 |
| Yes | 113,143 (20.44) | 112,741 (20.43) | 402 (26.29) | |
| Age at menarche, year | ||||
| Mean ± SD | 14.27±1.61 | 14.27±1.61 | 14.63±1.67 | <0.0001 |
| <13 | 68,602 (12.40) | 68,465 (12.41) | 137 (8.96) | <0.0001 |
| 13 | 113,617 (20.53) | 113,348 (20.54) | 269 (17.59) | |
| 14 | 145,319 (26.26) | 144,956 (26.26) | 363 (23.74) | |
| 15 | 105,217 (19.01) | 104,906 (19.01) | 311 (20.34) | |
| ≥16 | 120,679 (21.81) | 120,230 (21.78) | 449 (29.37) | |
| Menopause status‡, No (%†) | ||||
| Natural menopause | 350,273 (63.29) | 349,073 (63.25) | 1,200 (78.48) | <0.0001 |
| Surgical menopause | 14,492 (2.62) | 14,411 (2.61) | 81 (5.30) | |
| Age at menopause‡, year | ||||
| Mean ± SD | 49.41±3.17 | 49.41±3.17 | 49.69±3.36 | 0.0028 |
| <45 | 20,636 (5.66) | 20,558 (5.66) | 78 (6.09) | <0.0001 |
| 45–49 | 126,294 (34.62) | 125,909 (34.64) | 385 (30.05) | |
| 50–54 | 200,368 (54.93) | 199,631 (54.92) | 737 (57.53) | |
| ≥55 | 17,467 (4.79) | 17,386 (4.78) | 81 (6.32) | |
| Reproductive period‡, year | ||||
| Mean ± SD | 34.98±3.50 | 34.98±3.49 | 34.98±3.61 | 0.9929 |
| <30 | 23,099 (6.33) | 23,007 (6.33) | 92 (7.18) | <0.0001 |
| 30–34 | 116,577 (31.96) | 116,175 (31.96) | 402 (31.38) | |
| 35–39 | 199,028 (54.56) | 198,338 (54.57) | 690 (53.86) | |
| ≥40 | 26,061 (7.14) | 25,964 (7.14) | 97 (7.57) | |
| Age at first live birth, year | ||||
| Mean ± SD | 24.85±4.70 | 24.85±4.70 | 25.23±4.66 | 0.0015 |
| Nulliparous | 12,642 (2.28) | 12,611 (2.28) | 31 (2.03) | <0.0001 |
| <25 | 200,009 (36.14) | 199,540 (36.15) | 469 (30.67) | |
| 25–29 | 303,569 (54.85) | 302,668 (54.84) | 901 (58.93) | |
| ≥30 | 37,214 (6.72) | 37,086 (6.72) | 128 (8.37) | |
| Duration of breastfeeding, month | ||||
| Mean ± SD | 12.46±8.68 | 12.46±8.68 | 12.31±7.98 | <0.0001 |
| 0 | 60,885 (11.00) | 60,694 (11.00) | 191 (12.49) | <0.0001 |
| 1–12 | 322,508 (58.27) | 321,545 (58.26) | 963 (62.98) | |
| ≥13 | 170,041 (30.72) | 169,666 (30.74) | 375 (24.53) | |
| Benign breast disease, No (%†) | ||||
| No | 379,377 (68.55) | 378,388 (68.56) | 989 (64.68) | 0.0011 |
| Yes | 174,057 (31.45) | 173,517 (31.44) | 540 (35.32) | |
| Surgeries on the reproductive system, No (%†) | ||||
| No | 474,009 (85.65) | 472,716 (85.65) | 1,293 (84.57) | 0.2262 |
| Yes | 79,425 (14.35) | 79,189 (14.35) | 236 (15.43) | |
| Histology type§ | ||||
| Adenocarcinoma | NA | NA | 1,202 (91.20) | NA |
| Squamous cell carcinomas | NA | NA | 55 (4.17) | |
| Small-cell carcinoma | NA | NA | 36 (2.73) | |
| Others | NA | NA | 236 (1.90) | |
†, column percentage; ‡, among postmenopausal women only; §, 211 lung cancer cases without information on histological type. SD, standard derivation; BMI, body-mass index.