Table 3. Baseline characteristics of the study subjects between the case and control groups.
| Groups | Case group, n (%) | Control group, n (%) | P |
|---|---|---|---|
| Total | 712 | 783 | |
| Age (years) | |||
| ≥40 | 591 (83.01 ) | 673 (85.95) | 0.132 |
| <40 | 121 (16.99) | 110 (14.05) | |
| Age of menarche (years) | |||
| ≥13 | 495 (69.52) | 477 (60.92) | <0.001 |
| <13 | 217 (30.48) | 306 (39.08) | |
| Menopausal status | |||
| Premenopause | 81 (11.38) | 292 (37.29) | <0.001 |
| Postmenopause | 631 (88.62) | 491 (62.71) | |
| Tumor size (cm) | |||
| ≤2.0 | 323 ( 45.37) | ||
| 2.1–4 | 329 (46.21) | ||
| >4 | 60 (8.43) | ||
| Pathological type | |||
| IDC | 618 (86.80) | ||
| ILC | 31 (4.35) | ||
| Other | 63 (8.85) | ||
| Lymph node metastasis | |||
| Negative | 334 (46.91) | ||
| Positive | 378 (53.09) | ||
| Immunohistochemical indexes | |||
| ER (−) | 176 (24.72) | ||
| ER (+) | 536 (75.28) | ||
| PR (−) | 168 (23.60) | ||
| PR (+) | 544 (76.41) | ||
| HER2 status | |||
| Negative | 361 (50.70) | ||
| Positive | 351 (49.30) | ||
| FDRs with breast cancer | |||
| Yes | 251 (35.25) | ||
| No | 461 (64.75) | ||
| Clinical staging | 654 (91.85) | ||
| I/II | |||
| III/IV | 58 (8.15) | ||
| Subtypes of breast cancer | |||
| Triple negative | 133 (18.68) | ||
| Non-triple negative | 579 (81.32) | ||
| Metastasis situation | |||
| Distant metastasis | 154 (21.63) | ||
| Primary lesion | 558 (78.37) |
Abbreviations: FDR, first-degree relative; IDC, invasive ductal carcinoma; ILC, invasive lobular carcinoma.