Table 1.
Patient characteristics
| All (n = 1729) N (%) |
HER2-0 (n = 770) N (%) |
HER2-low (n = 608) N (%) |
HER2+ (n = 351) N (%) |
P HER2-low versus HER2-0 | |||||
|---|---|---|---|---|---|---|---|---|---|
| Median age (range)* | 63 (24–97) | 62 (27–97) | 64 (26–95) | 61 (24–94) | 0.017‡ | ||||
| Stage at initial diagnosis | |||||||||
| Stage I–III | 1119 | (64.7) | 536 | (69.6) | 388 | (63.8) | 195 | (55.6) | 0.066 |
| DFS < 24 months | 366 | (32.7) | 179 | (33.4) | 119 | (30.7) | 68 | (34.9) | |
| DFS ≥ 24 months | 696 | (62.2) | 328 | (61.2) | 253 | (65.2) | 115 | (59) | |
| DFS NA** | 57 | (5.1) | 29 | (5.4) | 16 | (4.1) | 12 | (6.2) | |
| De novo metastatic | 602 | (34.8) | 231 | (30.0) | 217 | (35.7) | 154 | (43.9) | |
| Unknown | 8 | (0.5) | 3 | (0.4) | 3 | (0.5) | 2 | (0.6) | |
| Menopausal status* | |||||||||
| Postmenopausal | 1148 | (66.4) | 501 | (65.1) | 429 | (70.6) | 218 | (62.1) | 0.029 |
| Premenopausal | 226 | (13.1) | 108 | (14.0) | 60 | (9.9) | 58 | (16.5) | |
| Unknown | 336 | (19.4) | 154 | (20.0) | 109 | (17.9) | 73 | (20.8) | |
| Male*** | 19 | (1.1) | 7 | (0.9) | 10 | (1.6) | 2 | (0.6) | |
| Metastatic sites* | |||||||||
| Visceral disease | 836 | (48.4) | 337 | (43.8) | 279 | (45.9) | 220 | (62.7) | 0.464 |
| Non-visceral disease only | 893 | (51.6) | 433 | (56.2) | 329 | (54.1) | 131 | (37.3) | |
| Number of metastatic sites* | |||||||||
| Median (range) | 1 | (1–9) | 1 | (1–6) | 1 | (1–8) | 1 | (1–9) | 0.793 |
| 1 | 951 | (55) | 432 | (56.1) | 332 | (54.6) | 187 | (53.3) | |
| 2–3 | 661 | (38.2) | 288 | (37.4) | 232 | (38.2) | 141 | (40.2) | |
| ≥ 4 | 117 | (6.8) | 50 | (6.5) | 44 | (7.2) | 23 | (6.6) | |
| Hormone-receptor (HR) status | |||||||||
| Positive | 1266 | (73.2) | 554 | (71.9) | 504 | (82.9) | 208 | (59.3) | < 0.001 |
| Negative | 463 | (26.8) | 216 | (28.1) | 104 | (17.1) | 143 | (40.7) | |
| Histologic subtype | |||||||||
| No special type (NST) | 1205 | (69.7) | 503 | (65.3) | 433 | (71.2) | 269 | (76.6) | 0.010 |
| Invasive lobular | 228 | (13.2) | 129 | (16.8) | 80 | (13.2) | 19 | (5.4) | |
| Other | 224 | (13.0) | 101 | (13.1) | 82 | (13.5) | 41 | (11.7) | |
| Unknown | 72 | (4.2) | 37 | (4.8) | 13 | (2.1) | 22 | (6.3) | |
| Grade | |||||||||
| 1 | 70 | (4.0) | 36 | (4.7) | 29 | (4.8) | 5 | (1.4) | 0.032 |
| 2 | 751 | (43.4) | 314 | (40.8) | 295 | (48.5) | 142 | (40.5) | |
| 3 | 645 | (37.3) | 293 | (38.1) | 202 | (33.2) | 150 | (42.7) | |
| Unknown | 263 | (15.2) | 127 | (16.5) | 82 | (13.5) | 54 | (15.4) | |
| Treatment for early stage | |||||||||
| (Neo)adj. chemotherapy | 705 | (63.0) | 337 | (62.9) | 226 | (58.2) | 142 | (72.8) | 0.176 |
| (Neo)adj. trastuzumab ± pertuzumab | 133 | (11.9) | 13 | (2.4) | 17 | (4.4) | 103† | (52.8)† | 0.142 |
| Adj. endocrine therapy (HR+ only) | 623 | (78.9) | 299 | (79.7) | 245 | (79.8) | 79 | (73.1) | 1.000 |
| Treatment for metastatic disease | |||||||||
| Chemotherapy | 1161 | (67.1) | 499 | (64.8) | 378 | (62.2) | 284 | (80.9) | 0.341 |
| Trastuzumab | 315 | (18.2) | 12 | (1.6) | 29 | (4.8) | 274 | (78.1) | 0.001 |
| Pertuzumab | 170 | (9.8) | 5 | (0.6) | 20 | (3.3) | 145 | (41.3) | 0.001 |
| T-DM1 | 105 | (6.1) | 5 | (0.6) | 8 | (1.3) | 92 | (26.2) | 0.322 |
| Lapatinib | 119 | (6.9) | 3 | (0.4) | 9 | (1.5) | 107 | (30.5) | 0.061 |
| Endocrine therapy (HR+ only) | 1033 | (81.6) | 465 | (83.9) | 429 | (85.1) | 139 | (66.8 | 0.655 |
| CDK4/6 inhibitor (HR+ only) | 443 | (35.0) | 213 | (38.4) | 215 | (42.7) | 15 | (7.2) | 0.183 |
Statistically significant p-values are highlighted in bold
*At diagnosis of metastatic disease
**No surgery or incomplete surgery date
***Not included in subgroup comparison with chi-square tests
†17 patients did not receive any (neo-)adjuvant therapy, 11 patients were diagnosed before trastuzumab was available, 20 patients had HER2- primary tumors but HER2+ metastatic disease
‡Calculated with Wilcoxon test. All other p-values result from Chi-square tests