Table 1.
Characteristics of the development and validation cohorts
| Characteristic | (n = 466) | (n = 179) | (n = 90) | (n = 197) | |
|---|---|---|---|---|---|
| Total | Development cohort | Internal validation cohort | External validation cohort | p value | |
| Age (y)a | 52.8 ± 11.7 | 50.3 ± 10.8 | 54.6 ± 11.3 | 54.4 ± 12.2 | .001 |
| Clinical T stage | |||||
| T1 | 242 (51.9%) | 89 (49.7%) | 48 (53.3%) | 105 (53.3%) | .75 |
| T2 | 224 (48.1%) | 90 (50.3%) | 42 (46.7%) | 92 (46.7%) | |
| Ultrasound tumor size (cm)b | 2.1 ± 0.9 | 2.0 (1.4–2.6) | 1.9 (1.4–2.3) | 1.9 (1.4–2.5) | .45 |
| Histologic type | .81 | ||||
| Invasive ductal carcinoma | 378 (81.1%) | 143 (79.9%) | 71 (78.9%) | 164 (83.2%) | |
| Invasive lobular carcinoma | 21 (4.5%) | 10 (5.6%) | 4 (4.4%) | 7 (3.6%) | |
| Other types | 67 (14.4%) | 26 (14.5%) | 15 (16.7%) | 26 (13.2%) | |
| Histologic grade | .01 | ||||
| Low | 63 (13.5%) | 27 (15.1%) | 15 (16.7%) | 21 (10.7%) | |
| Intermediate | 260 (55.8%) | 107 (59.8%) | 58 (64.4%) | 95 (48.2%) | |
| High | 126 (27.0%) | 41 (22.9%) | 17 (18.9%) | 68 (34.5%) | |
| Not applicable | 17 (3.6) | 4 (2.2%) | 0 (0.0%) | 13 (6.6%) | |
| Lymphovascular invasion | < .001 | ||||
| No | 363 (80.3%) | 153 (85.5%) | 79 (87.8%) | 142 (72.1%) | |
| Yes | 92 (19.7%) | 26 (14.5%) | 11 (12.2%) | 55 (27.9%) | |
| ER | .001 | ||||
| Negative | 100 (21.5%) | 30 (16.8%) | 12 (13.3%) | 58 (29.4%) | |
| Positive | 366 (78.5%) | 149 (83.2%) | 78 (86.7%) | 139 (70.6%) | |
| PR | .01 | ||||
| Negative | 145 (31.1%) | 46 (25.7%) | 23 (25.6%) | 76 (38.6%) | |
| Positive | 321 (68.9%) | 133 (74.3%) | 67 (74.4%) | 121 (61.4%) | |
| Not applicable | |||||
| HER2 | .04 | ||||
| Negative | 374 (80.3%) | 148 (82.7%) | 78 (86.7%) | 148 (75.1%) | |
| Positive | 92 (19.7%) | 31 (17.3%) | 12 (13.3%) | 49 (24.9%) | |
| Type of breast surgery | < .001 | ||||
| Breast conserving surgery | 181 (38.8%) | 86 (48.0%) | 53 (58.9%) | 42 (21.3%) | |
| Mastectomy | 285 (61.2%) | 93 (52.0%) | 37 (41.1%) | 155 (78.7%) | |
| Contrast agent | |||||
| Sonovue | 254 (54.5%) | 150 (83.8%) | 0 (0%) | 104 (52.8%) | < .001 |
| Sonazoid | 212 (45.5%) | 29 (16.2%) | 90 (100%) | 93 (47.2%) | |
| Mean number of SLNs by blue or green dyesc | 3.0 (0.0–12.0) | 4 (0–12) | 4 (1–11) | 2 (0–6) | < .001 |
| Mean number of SLNs by CE lymphatic USc | 1 (1–5) | 1 (1–5) | 1 (1–4) | 1 (1–4) | < .001 |
| SLN biopsy results | .54 | ||||
| No metastasis | 326 (70.0%) | 119 (66.5%) | 65 (72.2%) | 142 (72.1%) | |
| Micrometastasis | 11 (2.4%) | 3 (1.7%) | 2 (2.2%) | 6 (3.0%) | |
| Macrometastasis | 129 (27.7%) | 57 (31.8%) | 23 (25.6%) | 49 (24.9%) | |
| Type of axillary surgery | .36 | ||||
| SLN biopsy | 350 (75.1%) | 129 (72.1%) | 72 (80.0%) | 149 (75.6%) | |
| ALN dissection | 116 (24.9%) | 50 (27.9%) | 18 (20.0%) | 48 (24.4%) | |
| Number of metastatic ALN | .91 | ||||
| 0 | 326 (70.0%) | 119 (66.5%) | 65 (72.2%) | 142 (72.1%) | |
| 1 | 56 (12.0%) | 25 (14.0%) | 10 (11.1%) | 21 (10.7%) | |
| 2 | 33 (7.1%) | 14 (7.8%) | 5 (5.6%) | 14 (7.1%) | |
| ≥ 3 | 51 (10.9%) | 21 (11.7%) | 10 (11.1%) | 20 (10.2%) | |
Unless otherwise specified, data are numbers of patients, with percentages in parentheses
ER estrogen receptor, PR progesterone receptor, HER2 human epidermal growth factor receptor 2, SLN sentinel lymph node, ALN axillary lymph node
aData are means ± standard deviations
bData are medians, with interquartile range in parentheses
cData are medians, with ranges in parentheses