Table 2.
Local control (LC) outcomes according to clinical factors
| N (%) | 2-year LC | P-value | ||
|---|---|---|---|---|
| Entire | 49.4% | |||
| Age | < 45 years | 33 (24.8) | 48.7% | 0.830 |
| ≥ 45 years | 100 (75.2) | 50.0% | ||
| Subtype | HR positive/HER2 negative | 48 (36.1) | 56.0% | 0.210 |
| HR positive/HER2 positive | 19 (14.3) | 34.3% | ||
| HR negative/HER2 positive | 19 (14.3) | 30.0% | ||
| TN | 47 (35.3) | 57.1% | ||
| Treatment era | 2010–2015 | 52 (39.1) | 42.6% | 0.087 |
| 2016–2021 | 81 (60.9) | 55.8% | ||
| Previous systemic treatments | ≤ 2 lines | 72 (54.1) | 62.7% | < .001 |
| > 2 lines | 61 (45.9) | 27.6% | ||
| Interval from diagnosis to PRT | ≤ 1 year | 65 (48.9) | 58.5% | 0.053 |
| > 1 year | 68 (51.1) | 38.9% | ||
| No vs. Yes | ||||
| Disease extent at PRT | LN | 61 (45.9) | 55.7% vs. 42.5% | 0.110 |
| Liver | 26 (19.5) | 50.4% vs. 44.1% | 0.260 | |
| Lung | 59 (44.4) | 46.2% vs. 54.9% | 0.810 | |
| Bone | 72 (54.1) | 52.1% vs. 48.5% | 0.860 | |
| Brain | 5 (3.8) | 50.9% vs. 0.0% | < .001 | |
| Number of metastases | Oligometastasis (≤ 5 lesions) | 13 (9.8) | 66.7% | 0.330 |
| Polymetastasis (> 5 lesions) | 120 (90.2) | 47.6% | ||
| Status | De novo stage IV | 30 (22.6) | 64.2% | 0.076 |
| Progressive stage IV | 76 (57.1) | 46.1% | ||
| Recurrent stage IV | 27 (20.3) | 45.1% | ||
| Disease burden (outside breast) | SD | 104 (78.2) | 54.1% | 0.003 |
| PD or mixed response | 29 (21.8) | 24.4% | ||
| Reason for breast PRT | Symptom (bleeding, pain) | 51 (38.3) | 62.3% | 0.180 |
| Radiologic progression | 82 (61.7) | 42.1% | ||
| Concurrent treatment | No | 50 (37.6) | 54.3% | 0.360 |
| Endocrine therapy | 27 (20.3) | 59.2% | ||
| Anti-HER2 therapy | 10 (7.5) | 50.0% | ||
| Cytotoxic chemotherapy | 46 (34.6) | 34.8% | ||
| Gross tumor volume | < 1260 cm3 | 107 (80.5) | 50.2% | 0.110 |
| ≥ 1260 cm3 | 26 (19.5) | 46.2% | ||
| PRT dose (EQD2) | < 63 Gy | 72 (54.1) | 42.9% | 0.010 |
| ≥ 63 Gy | 61 (45.9) | 67.7% | ||
| PRT modality | 3D-CRT | 74 (55.6) | 44.5% | 0.330 |
| IMRT/Proton | 59 (44.4) | 56.5% |
HR Hormone receptor, HER2 Human epidermal growth factor receptor 2, TN Triple-negative, LN Lymph node, SD Stable disease, PD Progressive disease, PRT Palliative radiation therapy, EQD2 Equivalent dose in 2 Gy fractions (α/β = 3.5), 3D-CRT, 3 dimensional-conformal radiation therapy; IMRT, intensity-modulated radiation therapy