Table 2. Baseline clinicopathological characteristics.
| Characteristics | n (%) | P | ||
| Training group (N=1,074) |
Internal validation group (N=640) |
External validation group (N=427) |
||
| IDC, invasive ductal carcinoma; ER, estrogen receptor; PR, progesterone receptor; NA, not available; HER2, human epidermal receptor 2; TNBC, triple negative breast cancer; BCS, breast conversing surgery; SLNB, sentinel lymph node biopsy; ALND, axillary lymph node dissection; NAT, neo-adjuvant treatment. *, HER2 status is according to core needle biopsy specimen before NAC. | ||||
| Age (year) | 0.196 | |||
| <50 | 495 (46.1) | 318 (49.7) | 215 (50.4) | |
| ≥50 | 579 (53.9) | 322 (50.3) | 212 (49.6) | |
| Menstruation | 0.360 | |||
| Pre-menopausal | 560 (52.1) | 352 (55.0) | 237 (55.5) | |
| Post-menopausal | 514 (47.9) | 288 (45.0) | 190 (44.5) | |
| Histology | 0.319 | |||
| IDC | 1,027 (95.6) | 603 (94.2) | 402 (94.1) | |
| Non-IDC | 47 (4.4) | 37 (5.8) | 25 (5.9) | |
| Grade | 0.450 | |||
| I | 171 (15.9) | 92 (14.4) | 64 (15.0) | |
| II | 624 (58.1) | 374 (58.4) | 266 (62.3) | |
| III | 279 (26.0) | 174 (27.2) | 97 (22.7) | |
| ER | 0.364 | |||
| Negative | 348 (32.4) | 207 (32.3) | 123 (28.8) | |
| Positive | 726 (67.6) | 433 (67.7) | 304 (71.2) | |
| PR | 0.252 | |||
| Negative | 432 (40.2) | 248 (38.8) | 152 (35.6) | |
| Positive | 642 (59.8) | 392 (61.3) | 275 (64.4) | |
| Ki67 | 0.543 | |||
| <14% | 138 (12.8) | 71 (11.1) | 52 (12.2) | |
| ≥14% | 925 (86.1) | 565 (88.2) | 368 (86.2) | |
| NA | 11 (1.1) | 4 (0.7) | 7 (1.6) | |
| HER2* | 0.754 | |||
| HER2-zero | 223 (20.8) | 123 (19.2) | 87 (20.4) | |
| HER2-low | 496 (46.2) | 293 (45.8) | 206 (48.2) | |
| HER2-amplified | 355 (33.1) | 224 (35.0) | 134 (31.4) | |
| Primary phenotype | 0.550 | |||
| Luminal-A | 75 (7.0) | 30 (4.7) | 26 (6.1) | |
| Luminal-B/HER2- negative |
472 (43.9) | 282 (44.1) | 205 (48.0) | |
| Luminal-B/HER2- positive |
217 (20.2) | 140 (21.9) | 87 (20.4) | |
| HER2-amplified | 138 (12.8) | 84 (13.1) | 47 (11.0) | |
| TNBC | 172 (16.0) | 104 (16.3) | 62 (14.5) | |
| Breast surgery | 0.212 | |||
| Mastectomy | 845 (88.0) | 545 (85.2) | 375 (87.8) | |
| BCS | 129 (12.0) | 95 (14.8) | 52 (12.2) | |
| Axillary surgery | 0.036 | |||
| SLNB | 90 (8.4) | 74 (11.6) | 32 (7.5) | |
| ALND±SLNB | 984 (91.6) | 566 (88.4) | 395 (92.5) | |
| Clinical stage | 0.315 | |||
| I | 59 (5.5) | 38 (5.9) | 24 (5.6) | |
| IIA | 269 (25.0) | 171 (26.7) | 121 (28.3) | |
| IIB | 414 (38.5) | 249 (38.9) | 158 (37.0) | |
| IIIA | 158 (14.7) | 88 (13.8) | 67 (15.7) | |
| IIIB | 54 (5.0) | 42 (6.6) | 14 (3.3) | |
| IIIC | 120 (11.2) | 52 (8.1) | 43 (10.1) | |
| Pathologic stage | 0.207 | |||
| 0 | 242 (22.5) | 157 (24.5) | 98 (23.0) | |
| I | 156 (14.5) | 101 (15.8) | 80 (18.7) | |
| IIA | 247 (23.0) | 167 (26.1) | 90 (21.1) | |
| IIB | 94 (8.8) | 41 (6.4) | 24 (5.6) | |
| IIIA | 183 (17.0) | 97 (15.2) | 72 (16.9) | |
| IIIB | 27 (2.5) | 12 (1.9) | 9 (2.1) | |
| IIIC | 125 (11.6) | 65 (10.2) | 54 (12.6) | |
| Neo-adjuvant anti-HER2 therapy | 0.445 | |||
| Yes | 355 (33.1) | 224 (35.0) | 134 (31.4) | |
| No | 720 (66.9) | 417 (65.0) | 293 (68.6) | |
| NAT cycle | 0.225 | |||
| 4−6 | 645 (60.1) | 403 (63.0) | 275 (64.4) | |
| >6 | 429 (39.9) | 237 (37.0) | 152 (35.6) | |