Table 1.
Patient baseline demographic and disease characteristics.
| Characteristic | Patients (n = 397) |
|---|---|
| Age | |
| Median (range) | 55 (28–85) |
| Age, n (%) | |
| <65 years | 293 (73.80) |
| ≥65 years | 104 (26.20) |
| Menopausal status at study entry, n (%) | |
| Premenopausal | 91 (22.92) |
| Perimenopausal | 43 (10.83) |
| Postmenopausal | 263 (66.25) |
| ECOG performance status, n (%) | |
| 0–1 | 320 (80.60) |
| ≥2 | 77 (19.40) |
| Disposition of diagnosis, n (%) | |
| De novo, newly diagnosed stage IV | 90 (22.67) |
| Recurrent from earlier stages, stages I–III | 307 (77.33) |
| Pathology | |
| Invasive ductal carcinoma (IDC) | 194 (48.87) |
| Invasive lobular carcinoma (ILC) | 51 (12.85) |
| Other | 152 (38.29) |
| Expression of progesterone receptor (PR) | |
| <20% | 148 (37.28) |
| ≥20% | 242 (60.96) |
| Unknown | 7 (1.76) |
| Bone involvement, n (%) | |
| Bone + other metastases | 144 (36.27) |
| Bone only | 72 (18.14) |
| Visceral disease †, n (%) | |
| No | 198 (49.87) |
| Yes | 199 (50.13) |
| Liver metastases | 98 (24.69) |
| Lung metastases | 144 (36.27) |
| Number of sites of metastasis | |
| Median (range) | 2 (1.73–1.96) |
| Distribution, n (%) | |
| <2 | 187 (47.10) |
| ≥2 | 210 (52.90) |
| Prior adjuvant chemotherapy, n (%) | |
| Yes | 252 (63.48) |
| No | 51 (12.85) |
| Not reported | 4 (1.01) |
| Prior adjuvant ET, n (%) | |
| Yes | 253 (63.73) |
| No | 50 (12.59) |
| Not reported | 4 (1.01) |
| Sensitivity to ET *, n (%) | |
| Primary resistance | 72 (18.14) |
| Secondary resistance | 231 (58.19) |
| ET naïve | 81 (20.40) |
| Not reported | 13 (3.27) |
| Line of ET before CDK 4/6i treatment | |
| 1L | 217 (54.66) |
| ≥2L | 178 (44.84) |
| Unknown | 2 (0.50) |
1L, first line; 2L, second line; ET, endocrine therapy. † Metastases of brain, liver, and/or lung/pleura. * The definition of sensitivity to ET is consistent with ABC6. Primary endocrine resistance exists if a relapse occurs within 2 years after adjuvant endocrine therapy (ET) or if progression occurs within 6 months during first-line ET in advanced cancer. If primary resistance is excluded, secondary endocrine resistance can be assumed.