Clinical Study
Reproductive Risk Factors Associated with Breast Cancer Molecular Subtypes among Young Women in Northern China
Table 1
Characteristics of the participants in the young and older groups.
| | Characteristic | Overall participants | | Controls () | ≤40 years () | value | Controls () | >40 years () | value |
| | Mean age, years (SD, range) | 35.38 (4.01, 21-40) | 34.90 (4.18, 20-40) | 0.121 | 53.36 (8.27, 41-70) | 53.14 (8.37, 41-70) | 0.364 | | Mean age at menarche, years (SD, range) | 13.83 (1.39, 10-19) | 13.73 (1.56, 9-19) | 0.002 | 14.45 (1.66, 9-21) | 14.41 (1.72, 10-21) | 0.021 | | Among parous women | 931 (94.7%) | 645 (90.0%) | <0.001 | 3142 (98.2%) | 2979 (96.9) | 0.001 | | Mean number of completed pregnancies (SD) | 1.44 (0.66) | 1.38 (0.53) | 0.001 | 1.70 (0.84) | 1.71 (0.83) | 0.005 | | Mean age at first completed pregnancy (SD) | 25.40 (3.25) | 25.46 (3.04) | 0.481 | 24.59 (3.18) | 24.71 (3.16) | 0.368 | | Ever breastfed | 865 (92.9%) | 577 (89.5%) | 0.016 | 2964 (94.3%) | 2767 (92.9%) | 0.020 | | Mean duration of breastfeeding among those who breastfed, months (SD) | 16.83 (10.35) | 16.45 (10.09) | 0.176 | 25.21 (19.52) | 24.76 (15.88) | <0.001 | | Duration of oral contraceptive use | 136 (13.8%) | 134 (18.7%) | 0.007 | 458 (14.3%) | 495 (16.1%) | 0.049 | | Mean body mass index (SD) | 22.87 (2.73) | 23.51 (3.10) | <0.001 | 23.74 (2.76) | 24.27 (2.61) | 0.001 | | First-degree family history of breast cancer | 40 (4.1%) | 35 (4.9%) | 0.421 | 185 (5.8%) | 166 (5.4%) | 0.507 | | Subtype of breast cancer | | | | | | | | Luminal A | | 86 (12.0) | | | 1080 (35.1) | | | Luminal B | | 420 (58.6) | | | 1366 (44.4) | | | HER2 enriched | | 75 (10.4) | | | 316 (10.3) | | | TNBC | | 136 (19.0) | | | 313 (10.2) | | | Annual recruitment number | | | | | | | | 2012 | 129 | 99 | | 485 | 474 | | | 2013 | 145 | 108 | | 516 | 500 | | | 2014 | 176 | 130 | | 534 | 504 | | | 2015 | 165 | 121 | | 525 | 509 | | | 2016 | 172 | 122 | | 557 | 535 | | | 2017 | 196 | 137 | | 582 | 553 | |
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