Table 3.
Associations Between Left- vs Right-Sided RT for Breast Cancer and CAD, Stratified by Lifestyle Factors
| Laterality of RT | N | Total Cardiac Events | HRa (95% CI) | P Value for Heterogeneity | |
|---|---|---|---|---|---|
| Overallb | Right | 466 | 14 | Reference | |
| Left | 506 | 32 | 2.5 (1.3-4.7) | ||
| Age at breast cancer diagnosis, y | |||||
| <45 | Right | 182 | 7 | Reference | 0.24 |
| Left | 214 | 11 | 1.6 (0.6-4.2) | ||
| 45-54 | Right | 284 | 7 | Reference | |
| Left | 292 | 21 | 3.5 (1.5-8.3) | ||
| Lifetime smoking history | |||||
| Ever | Right | 175 | 8 | Reference | 0.53 |
| Left | 215 | 16 | 1.7 (0.7-4.0) | ||
| Never | Right | 291 | 6 | Reference | |
| Left | 291 | 16 | 3.3 (1.3-8.6) | ||
| BMI at breast cancer diagnosis, kg/m2 | |||||
| <25 | Right | 305 | 8 | Reference | 0.77 |
| Left | 325 | 16 | 2.4 (1.0-5.6) | ||
| ≥25 | Right | 161 | 6 | Reference | |
| Left | 181 | 16 | 2.8 (1.1-7.3) | ||
| Prior history of hypertension | |||||
| Present | Right | 50 | 3 | Reference | 0.94 |
| Left | 43 | 5 | 5.2 (0.9-28.3) | ||
| Absent | Right | 416 | 11 | Reference | |
| Left | 463 | 27 | 2.6 (1.3-5.2) | ||
| Prior history of hypercholesterolemia | |||||
| Present | Right | 22 | 2 | Reference | 0.67 |
| Left | 29 | 6 | 17.6 (1.7-187.7) | ||
| Absent | Right | 444 | 12 | Reference | |
| Left | 477 | 26 | 2.3 (1.2-4.6) | ||
| Any pre-existing risk factorc | |||||
| Present | Right | 208 | 10 | Reference | 0.66 |
| Left | 255 | 22 | 2.1 (0.9-4.4) | ||
| Absent | Right | 258 | 4 | Reference | |
| Left | 251 | 10 | 3.7 (1.1-12.2) | ||
| 2 or 3 pre-existing risk factorsc | |||||
| Present | Right | 34 | 3 | Reference | 0.45 |
| Left | 25 | 5 | 3.2 (0.3-30.9) | ||
| Absent | Right | 432 | 11 | Reference | |
| Left | 481 | 27 | 2.5 (1.2-5.1) | ||
| Year of breast cancer diagnosis | |||||
| 1985-1999 | Right | 371 | 12 | Reference | 0.93 |
| Left | 399 | 28 | 2.5 (1.2-4.9) | ||
| 2000-2008 | Right | 95 | 2 | Reference | |
| Left | 107 | 4 | 2.3 (0.4-12.6) | ||
| Follow-up time, yd | |||||
| 1-4.9 | Right | 51 | 1 | Reference | 0.94 |
| Left | 58 | 3 | 2.5 (0.2-26.8) | ||
| ≥5 | Right | 415 | 13 | Reference | |
| Left | 448 | 29 | 2.5 (1.3-4.9) | ||
BMI = body mass index; CAD = coronary artery disease; RT = radiation therapy.
HRs and 95% CIs are estimated in Cox proportional hazards regression.
Model is adjusted for age at breast cancer diagnosis, race/ethnicity, recruitment site, and WECARE Study phase. Participants were censored at age of diagnosis of a new primary cancer, breast cancer recurrence/metastasis, or the time of the cardiac survey.
Pre-existing risk factors include ever smoking history, prior hypertension, and prior hypercholesterolemia.
A woman's follow-up time is defined as the time from breast cancer diagnosis to the first to occur among the following: a new primary cancer, breast cancer recurrence/metastasis, diagnosis of coronary artery disease, or time of the follow-up survey.