Table 1.
Baseline characters.
| HER2-low (N = 144) | HER2-positive (N = 173) | Overall (N = 317) | |
|---|---|---|---|
| Median age (range) | 50.5 [30, 87] | 52.0 [28, 82] | 52.0 [28, 87] |
| Menopausal | 99 (68.8%) | 110 (63.6%) | 209 (65.9%) |
| ECOG PSa | |||
| 0-1 | 137 (95.1%) | 161 (93.1%) | 298 (94.0%) |
| ≥2 | 7 (4.9%) | 12 (6.9%) | 19 (6.0%) |
| Disease status | |||
| De novo stage IV | 25 (17.4%) | 36 (20.8%) | 61 (19.2%) |
| Recurring disease | 119 (82.6%) | 137 (79.2%) | 256 (80.8%) |
| Hormone receptor status | |||
| Positive | 94 (65.3%) | 75 (43.4%) | 169 (53.3%) |
| Negative | 50 (34.7%) | 98 (56.6%) | 148 (46.7%) |
| Baseline metastasis | |||
| Bone | 84 (58.3%) | 84 (48.6%) | 168 (53.0%) |
| Non regional lymph nodes | 75 (52.1%) | 104 (60.1%) | 179 (56.5%) |
| Lung | 65 (45.1%) | 83 (48.0%) | 148 (46.7%) |
| Liver | 75 (52.1%) | 63 (36.4%) | 138 (43.5%) |
| Brain | 32 (22.2%) | 67 (38.7%) | 99 (31.2%) |
| HER2 expression statusb | |||
| IHC 0 | 11 (7.6%)c | 0 (0%) | 11 (3.5%) |
| IHC 1+ | 54 (37.5%) | 0 (0%) | 54 (17.0%) |
| IHC 2+ and ISH-negative | 79 (54.9%) | 1 (0.6%) d | 80 (25.2%) |
| IHC 2+ and ISH-positive | 0 (0%) | 39 (22.5%) | 39 (12.3%) |
| IHC 3+ | 0 (0%) | 133 (76.9%) | 133 (42.0%) |
| Lines of previous systemic therapy in the metastatic setting | |||
| 0-1 | 28 (19.4%) | 51 (29.5%) | 79 (24.9%) |
| 2 | 37 (25.7%) | 36 (20.8%) | 73 (23.0%) |
| 3 | 24 (16.7%) | 16 (9.2%) | 40 (12.6%) |
| 4 | 19 (13.2%) | 22 (12.7%) | 41 (12.9%) |
| ≥5 | 36 (25.0%) | 48 (27.7%) | 84 (26.5%) |
| Median number of lines (range) | 4[1, 19] | 3 [1, 19] | 4 [1, 19] |
| Previous cancer therapy | |||
| CDK 4/6 inhibitors e | 72 (50.0%) | 9 (5.2%) | 81 (25.6%) |
| Taxel-based chemotherapy | 133 (92.4%) | 159 (91.9%) | 292 (92.1%) |
| Antibody drug conjugate (ADCs) | 29 (20.1%) | 79 (45.7%) | 108 (34.1%) |
| T-DM1 | 4 (2.8%) | 62 (35.8%) | 66 (20.8%) |
| Tubulin-inhibitor-payload ADCs | 18 (12.5%) | 79 (45.7%) | 97 (30.6%) |
| Topoisomerase-inhibitor-payload ADCs | 13 (9.0%) | 2 (1.2%) | 15 (4.7%) |
aPerformance status scores on the Eastern Cooperative Oncology Group (ECOG) scale range from 0 (no disability) to 5 (death).
bHER2-low expression of human epidermal growth factor receptor 2 was defined as a score of 1+ on immunohistochemical analysis or as an IHC score of 2+ and negative results on in situ hybridization (ISH).
cPatients had previous HER2 1+ or 2+ expression, and presented HER2 0 in the latest tumor biopsy.
dOne patient showed a negative result of HER2 FISH but HER2 enrich of PAM50 sub-type.
eCDK4/6 denotes cyclin-dependent kinases 4 and 6.
Abbreviations: ADC, antibody–drug conjugate; T-DXd, trastuzumab deruxtecan; HER2, human epidermal growth factor receptor 2; IHC, immunohistochemistry; tubulin-inhibitor-payload ADCs including trastuzumab emtansine and disitamab vedotin; topoisomerase-inhibitor-payload ADCs included sacituzumab govitecan.