TABLE 4.
Multivariate Cox Regression Analysis of Time to Ipsilateral Breast Tumor Recurrence*
| Variable | n | Events (IBTR) | HR | 95% CI | P value |
|---|---|---|---|---|---|
| Time to Initiation of RT | 0.015† | ||||
| ≤ 8 weeks | 790 | 75 | 1.00 | ||
| > 8 weeks–12 weeks | 380 | 25 | 0.80 | 0.51–1.27 | 0.35 |
| > 12 weeks | 124 | 18 | 1.92 | 1.14–3.24 | 0.014 |
| Menopausal Status | |||||
| Pre/peri | 494 | 64 | 1.00 | ||
| Post | 800 | 54 | 0.54 | 0.37–0.77 | 0.0009 |
| Presentation | |||||
| Clinical | 134 | 20 | 1.00 | ||
| Radiologic | 1160 | 98 | 0.68 | 0.42–1.10 | 0.12 |
| Necrosis | |||||
| Absent | 293 | 23 | 1.00 | ||
| Present | 1001 | 95 | 1.23 | 0.77–1.94 | 0.39 |
| RT dose | |||||
| Per 100 cGy | 1.01 | 0.97–104 | 0.77 | ||
| Endocrine Therapy | |||||
| No | 949 | 100 | 1.00 | ||
| Yes | 345 | 18 | 0.45 | 0.27–0.74 | 0.0018 |
Abbreviations: IBTR, ipsilateral breast tumor recurrence; HR, hazard ratio; CI, confidence interval; RT, radiation therapy
*
The multivariable model included 1294 patients with complete data and 118 IBTR events.
†
Type III Wald test for overall difference in IBTR event rate across the three RT timing groups.