Table 1.
Baseline characteristics of patients and breast cancer.
| Characteristics | Training set | Validation set | External test set | P value |
|---|---|---|---|---|
| No. patients | 489 | 114 | 90 | |
| Age (y) | 51 (27–83) | 52 (33–77) | 53 (26–84) | 0.162 |
| Tumor size on US (mm) | 21 (6–49) | 23 (6–50) | 20 (7–48) | 0.003 |
| Clinical T stage | 0.144 | |||
| T1 (<2 cm) | 220 (45.0%) | 40 (35.1%) | 41 (45.6%) | |
| T2 (2–5 cm) | 269 (55.0%) | 74 (64.9%) | 49 (54.4%) | |
| Menopausal status | 0.804 | |||
| premenopausal | 235 (48.1%) | 53 (46.5%) | 40 (44.4%) | |
| postmenopausal | 254 (51.9%) | 61 (53.5%) | 50 (55.6%) | |
| BI-RADS | 0.260 | |||
| 4A | 6 (1.2%) | 1 (0.9%) | 1 (1.1%) | |
| 4B | 93 (19.0%) | 15 (13.2%) | 23 (25.6%) | |
| 4C | 226 (46.2%) | 55 (48.2%) | 23 (25.6%) | |
| 5 | 164 (33.5%) | 43 (37.7%) | 43 (47.8%) | |
| Histologic type | 0.206 | |||
| IDC | 428 (87.5%) | 98 (86.0%) | 76 (84.4%) | |
| ILC | 20 (4.1%) | 2 (1.8%) | 5 (5.6%) | |
| Mixed | 29 (5.9%) | 10 (8.8%) | 3 (3.3%) | |
| Other | 12 (2.5%) | 4 (3.5%) | 6 (6.7%) | |
| ER status | 0.814 | |||
| positive | 410 (83.8%) | 95 (83.3%) | 73 (81.1%) | |
| negative | 79 (16.2%) | 19 (16.7%) | 17 (18.9%) | |
| PR status | 0.130 | |||
| positive | 404 (82.6%) | 87 (76.3%) | 68 (75.6%) | |
| negative | 85 (17.4%) | 27 (23.7%) | 22 (24.4%) | |
| HER2 status | 0.343 | |||
| positive | 123 (25.2%) | 35 (30.7%) | 20 (22.2%) | |
| negative | 366 (74.8%) | 79 (69.3%) | 70 (77.8%) | |
| Ki-67 | 0.863 | |||
| ≥20% | 344 (70.3%) | 81 (71.1%) | 61 (67.8%) | |
| ＜20% | 145 (29.7%) | 33 (28.9%) | 29 (32.2%) | |
| Molecular subtypes | 0.298 | |||
| Luminal | 431 (88.1%) | 100 (87.7%) | 74 (82.2%) | |
| Non-luminal | 58 (11.9%) | 14 (12.3%) | 16 (17.8%) |
Note: Age and tumor size on US were presented as median (range). Other data were presented as number and percentages. The Kruskal–Wallis rank sum test was used to compare the difference in age, tumor size on US, clinical T stage and BI-RADS. Chi-square test was used to compare the difference in menopausal status, ER, PR, HER2, Ki-67 and molecular subtypes. US, ultrasound; BI-RADS, breast imaging reporting and data system; IDC, Invasive ductal cancer; ILC, Invasive lobular cancer; Mixed, more than one histologic type in one tumor; Other, just one histologic type other than the IDC or ILC; ER, estrogen receptor; PR, progesterone receptor; HER2, human epidermal growth factor receptor 2.