Table 2.
Multivariate Cox analysis to estimate the association of treatment with the risk of subsequent iDCIS and iIBC.
| iDCIS | iIBC | |||||
|---|---|---|---|---|---|---|
| Age at DCIS (years) | Time since DCIS (years) | Treatment | Events (N)/at risk (N) | HR (95% CI) | Events (N)/at risk (N) | HR (95% CI) |
| <50 (N = 2143) | 0–5 | BCS + RT | 15/457 | Ref. | 17/457 | Ref. |
| BCS only | 57/474 | 3.2 (1.6–6.6) | 33/474 | 2.1 (1.4–3.2) | ||
| Mastectomya | – | – | 19 / 1212 | 0.4 (0.2–0.6) | ||
| 5–10 | BCS + RT | 8/419 | Ref. | 22/412 | Ref. | |
| BCS only | 12/386 | 2.5 (1.1–5.3) | 23/379 | 1.0 (0.7–1.5) | ||
| Mastectomya | – | – | 13/1161 | 0.1 (0.1–0.3) | ||
| ≥10 | BCS + RT | 17/383 | Ref. | 38/363 | Ref. | |
| BCS only | 4/353 | 0.7 (0.3–1.5) | 36/331 | 0.6 (0.4–0.9) | ||
| Mastectomya | – | – | 17/1108 | 0.1 (0.1v0.2) | ||
| ≥50 (N = 7902) | 0–5 | BCS + RT | 69/2147 | Ref. | 29/2147 | Ref. |
| BCS only | 201/2173 | 3.6 (2.6–4.8) | 137/2173 | 4.3 (3.0–6.0) | ||
| Mastectomya | – | – | 14/3582 | 0.3 (0.2–0.4) | ||
| 5–10 | BCS + RT | 26/1975 | Ref. | 63/1981 | Ref. | |
| BCS only | 63/1701 | 2.7 (1.8-4.1) | 119/1682 | 2.1 (1.6–2.8) | ||
| Mastectomya | – | – | 9/3314 | 0.1 (0.1–0.2) | ||
| ≥10 | BCS + RT | 10/1769 | Ref. | 70/1751 | Ref. | |
| BCS only | 15/1436 | 0.7 (0.4–1.3) | 94/1352 | 1.2 (0.9–1.6) | ||
| Mastectomya | – | – | 17/2957 | 0.1 (0.1–0.1) | ||
HR hazard ratio, 95% CI 95% confidence interval, Ref. reference category, BCS breast-conserving surgery, RT radiotherapy, iDCIS ipsilateral ductal carcinoma in situ, iIBC ipsilateral invasive breast cancer, DCIS ductal carcinoma in situ.
aInformation regarding mastectomy treatment was not available for iDCIS. Attained age was used as a primary timescale, adjusted for a period of initial DCIS diagnosis (1989–1998 versus 1999–2004) and age at DCIS diagnosis (<50 versus ≥50), including an age–treatment interaction term.