Table 3.
Radiotherapy effects on ipsilateral breast event (IBE) in each molecular subtype.
| Molecular Subtype |
Events/No. of cases |
5-year IBE incidence (%) |
Weighted Cox proportional hazards |
Non-weighted Cox proportional hazards |
Fine & Gray competing risks |
|||||
|---|---|---|---|---|---|---|---|---|---|---|
| RT | Non-RT | RT | Non-RT | *HR (95% CI) | P | *HR (95% CI) | P | *HR (95% CI) | P | |
| HR-HER2- | 6/243 | 2/56 | 1.9 | 1.8 | 0.768 (0.196–3.027) | 0.708 | 0.548 (0.133–2.264) | 0.406 | 0.642 (0.146–2.820) | 0.560 |
| HR-HER2+ | 14/390 | 4/108 | 3.6 | 4.1 | 1.131 (0.304–4.202) | 0.855 | 0.903 (0.298–2.740) | 0.858 | 0.954 (0.321–2.840) | 0.930 |
| HR+HER2+ | 16/824 | 8/262 | 2.0 | 3.5 | 0.530 (0.210–1.342) | 0.181 | 0.597 (0.233–1.527) | 0.282 | 0.616 (0.242–1.570) | 0.310 |
| HR+HER2- | 35/2,583 | 36/1,162 | 0.9 | 2.6 | 0.334 (0.207–0.539) | <0.001 | 0.346 (0.213–0.561) | <0.001 | 0.355 (0.219–0.577) | <0.001 |
Abbreviations: RT, radiotherapy; HR, hazard ratio; CI, confidence interval; IBE, ipsilateral breast event; HR, hormone receptor; HER2, human epidermal growth factor receptor-2.
*Note: In weighted Cox proportional hazards regression model, cases were weighted by inverse propensity score. These three multivariate regression models were adjusted by year of diagnosis, age, race, tumor size, grade, and histology subtype.