Left-Sided Breast Irradiation does not Result in Increased Long-Term Cardiac-Related Mortality Among Women Treated with Breast-Conserving Surgery

Standard therapy following lumpectomy for breast cancer has included adjuvant whole-breast radiotherapy. Recent, long-term studies have suggested a possible association between left-sided whole breast radiotherapy and long-term cardiac-related mortality. We sought to determine whether left-sided breast cancers treated with breast-conserving treatment have worse cardiac-related outcomes. The surveillance, epidemiology, and end results database was queried for female breast cancer cases diagnosed from 1990 to 1999. Subjects who underwent lumpectomy and adjuvant radiotherapy were included for study and grouped according to laterality. The primary outcome measure was the rate of cardiac-related mortality. Secondary outcome measures were overall and cancer-specific survival. A Cox proportional hazards model was constructed to analyze the primary outcome measure and included age, race, grade, stage, hormone receptor status, and histologic subtype. A total of 66,687 subjects were identified. These were divided equally by laterality groups: 33,866 left (50.8 %) and 32,801 right (49.2 %). Median follow-up was 15.5 years, and the groups were otherwise well-matched. Left-sided cancer was not associated with poorer survival for any of the metrics. Fifteen-year overall survival and disease-specific survival were 62.8 and 87.0 % for left-sided and 63.0 and 87.1 % for right-sided breast cancers, respectively (p = 0.260, p = 0.702). Rate of cardiac-related mortality at 5-, 10-, and 15-year follow-up were 1.5, 4.3, and 7.7 % for left-sided cancers and 1.6, 4.4, and 8.0 % for right-sided cancers, respectively (p = 0.435). In this large population-based study, women receiving left-sided external beam radiation for breast cancer did not have an increase in cardiac-related mortality.