Table 1. Major risk factors selected from the trial set of the Seoul Breast Cancer Study (SeBCS).
| Risk factors | Total set (n=4,574) | U50 (n=2,622) | O50 (n=1,952) | |||
|---|---|---|---|---|---|---|
| Cases (n=2,291) |
Controls (n=2,283) |
Cases (n=1,314) |
Controls (n=1,308) |
Cases (n=977) |
Controls (n=975) |
|
| Age of first full-term pregnancy, yr (No. %) | ||||||
| No children | 208 (9.08) | 183 (8.02) | 157 (11.95) | 161 (12.31) | 51 (5.22) | 22 (2.26) |
| <24 (early pregnancy) | 459 (20.03) | 579 (25.36) | 154 (11.72) | 231 (17.66) | 305 (31.22) | 348 (35.69) |
| 24 to 28 | 1,191 (51.99) | 1,157 (50.68) | 708 (53.88) | 667 (50.99) | 483 (49.44) | 490 (50.26) |
| ≥28 (late pregnancy) | 433 (18.9) | 364 (15.94) | 295 (22.45) | 249 (19.04) | 138 (14.12) | 115 (11.79) |
| Number of children, (No. %) | ||||||
| 0 (no childbirth) | 239 (10.43) | 204 (8.94) | 178 (13.55) | 176 (13.45) | 61 (6.24) | 28 (2.87) |
| 1 to 2 | 1,458 (63.64) | 1,392 (60.97) | 993 (75.57) | 965 (73.78) | 465 (47.6) | 427 (43.8) |
| ≥3 (many childbirths) | 594 (25.93) | 687 (30.09) | 143 (10.88) | 167 (12.77) | 451 (46.16) | 520 (53.33) |
| Age of menarche, yr (mean±SD) | 15.03±1.75 | 15.23±1.82 | 14.57±1.55 | 14.69±1.67 | 15.67±1.81 | 15.96±1.77 |
| Age of menarche, yr (No. %) | ||||||
| ≤15 (early menarche) | 1,492 (65.12) | 1,351 (59.18) | 1,006 (76.56) | 951 (72.71) | 486 (49.74) | 400 (41.03) |
| >15 (late menarche) | 799 (34.88) | 932 (40.82) | 308 (23.44) | 357 (27.29) | 491 (50.26) | 575 (58.97) |
| Body mass index (mean±SD) | 23.16±3.11 | 23.04±2.99 | 22.40±2.89 | 22.44±2.93 | 24.17±3.10 | 23.83±2.88 |
| Body mass index (No. %) | ||||||
| <25 (underweight woman) | 1,709 (74.6) | 1,753 (76.78) | 1,081 (82.27) | 1,087 (83.11) | 628 (64.28) | 666 (68.31) |
| 25 to 30 | 520 (22.7) | 486 (21.29) | 216 (16.44) | 202 (15.44) | 304 (31.11) | 284 (29.13) |
| ≥30 (overweight woman) | 62 (2.7) | 44 (1.93) | 17 (1.29) | 19 (1.45) | 45 (4.61) | 25 (2.56) |
| Family medical history of breast cancer (No. %) | ||||||
| Yes | 97 (4.23) | 52 (2.28) | 58 (4.41) | 30 (2.29) | 39 (3.99) | 22 (2.26) |
| No | 2,194 (95.77) | 2,231 (97.72) | 1,256 (95.59) | 1,278 (97.71) | 938 (96.01) | 953 (97.74) |
| Menopausal status (No. %) | ||||||
| Premenopausal | 165 (7.2) | 295 (12.92) | 112 (8.52) | 165 (12.61) | 53 (5.42) | 130 (13.33) |
| Postmenopausal | 2,126 (92.8) | 1,988 (87.08) | 1,202 (91.48) | 1,143 (87.39) | 924 (94.58) | 845 (86.67) |
| Regular mammography (No. %) | ||||||
| No | 1,275 (55.65) | 957 (41.92) | 709 (53.96) | 537 (41.06) | 566 (57.93) | 420 (43.08) |
| Regular | 1,016 (44.35) | 1,326 (58.08) | 605 (46.04) | 771 (58.94) | 411 (42.07) | 555 (56.92) |
| Regular exercise (No. %) | ||||||
| No | 1,429 (62.37) | 1,283 (56.2) | 801 (60.96) | 737 (56.35) | 628 (64.28) | 546 (56) |
| Regular | 862 (37.63) | 1,000 (43.8) | 513 (39.04) | 571 (43.65) | 349 (35.72) | 429 (44) |
| Estrogen duration, yr (mean±SD) | 28.57±7.46 | 27.80±7.14 | 24.61±5.54 | 24.40±5.48 | 33.88±6.32 | 32.35±6.56 |
| Estrogen duration, yr (No. %) | ||||||
| ≤10 | 13 (0.57) | 12 (0.53) | 11 (0.84) | 11 (0.84) | 2 (0.2) | 1 (0.1) |
| 10 to 15 | 61 (2.66) | 70 (3.07) | 56 (4.26) | 60 (4.59) | 5 (0.51) | 10 (1.03) |
| 15 to 20 | 230 (10.04) | 245 (10.73) | 217 (16.51) | 217 (16.59) | 13 (1.33) | 28 (2.87) |
| 20 to 25 | 393 (17.15) | 427 (18.7) | 343 (26.1) | 358 (27.37) | 50 (5.12) | 69 (7.08) |
| 25 to 30 | 560 (24.44) | 621 (27.2) | 432 (32.88) | 444 (33.94) | 128 (13.1) | 177 (18.15) |
| 30 to 35 | 626 (27.32) | 619 (27.11) | 247 (18.8) | 218 (16.67) | 379 (38.79) | 401 (41.13) |
| 35 to 40 | 296 (12.92) | 211 (9.24) | 8 (0.61) | 0 (0) | 288 (29.48) | 211 (21.64) |
| 40 to 45 | 66 (2.88) | 44 (1.93) | 0 (0) | 0 (0) | 66 (6.76) | 44 (4.51) |
| 45 to 50 | 32 (1.4) | 23 (1.01) | 0 (0) | 0 (0) | 32 (3.27) | 23 (2.36) |
| 50 to 55 | 7 (0.31) | 5 (0.22) | 0 (0) | 0 (0) | 7 (0.72) | 5 (0.51) |
| >55 | 7 (0.31) | 6 (0.26) | 0 (0) | 0 (0) | 7 (0.72) | 6 (0.62) |
U50, under 50 yr old group; O50, equal to or over 50 yr old group.