Abstract P1-10-13: Can the risk of radiation-induced cardiac disease in breast cancer be mitigated with cardiac-sparing techniques?
Authors: Smith TL , Mokhtech M , Bradley JA , Lightsey JL , Morris CG , Mendenhall NP 
Published: March 2017

Introduction: Data suggest that long-term survivors of breast cancer treated with radiation therapy (RT) have an increased risk of cardiac events despite an overall survival benefit, particularly women with left-sided breast cancers. We hypothesized that with cardiac-sparing radiation techniques there would be no difference in long-term cardiac risks between women with right- and left-sided breast cancers.

Materials and Methods: The outcomes of 775 consecutive women treated between 1984 and 1999 with breast-conserving therapy (BCT) (n=424) and post-mastectomy radiation therapy (PMRT) (n=351) for stage 0-3 breast cancer were assessed retrospectively through a review of medical records and contact with living patients. The choice of BCT vs PMRT was based on tumor board disposition and patient preference; mastectomy was recommended for multicentric or T3 breast cancers. Ninety-six percent of all node-positive patients received treatment to all nodal regions, including the internal mammary (IM), axillary (AX), and supraclavicular (SC) nodes. BCT patients had computed tomography-planned tangential breast radiation with photons with IM nodes treated within the tangent fields or with a separate en face electron field to minimize cardiac exposure. PMRT patients were treated with en face electron fields for the chest wall and IM for sparing of the lung and heart. The AX and SC nodes were treated with a matched anterior photon field with a posterior-anterior boost field (PAB) when necessary to achieve adequate dose in the AX with both BCT and PMRT. Overall, 411 patients were node-negative and 353 were node-positive. All patients have a minimum potential follow-up of 16.4 years; median actual follow-up for the BCT group was 15 years (range, 0.1-31.2) and for the PMRT group it was 9.5 years (range, 0.1-30.5).

Results: Overall survival (OS), cause-specific survival (CSS), and freedom from local-regional recurrence (FFLR) rates for the cohort at 15 years were 58.2%, 72.0%, and 90.8%, respectively. Rates of freedom from cardiac events (FFCE), pulmonary events, and second malignancy were 87.6%, 93.6%, and 86.3%, respectively. On multivariate analysis, OS was correlated with stage (p=.045), number of positive nodes (p=.002), age (p&lt;.0001), diabetes (p =.0021), and modality (p=.0017). Not surprisingly, 15-year survival for patients treated with BCT was better than for patients treated with PMRT (70.9% vs 59.7%; p&lt;.0001). CSS was associated with stage (p=.0207), number of positive nodes (p=.0409), and modality (p=.0003). FFLR was associated with number of positive nodes (p=.0484). FFCE was associated with pretreatment cardiac disease (p&lt;.0001), stage (p=.0461), and age (p=.0056), but not with either breast cancer laterality (p=.1906) or modality (BCT vs PMRT; p=.7487).

Discussion: Long-term disease control and survival outcomes were better in BCT than PMRT patients, likely due to selection criteria. Cardiac events were associated with pretreatment heart disease, older age, and stage, suggesting that this population may benefit from advanced radiation techniques that can further limit cardiac dose. Neither breast cancer laterality nor treatment modality was associated with cardiac events.

Citation Format: Smith TL, Mokhtech M, Bradley JA, Lightsey JL, Morris CG, Mendenhall NP. Can the risk of radiation-induced cardiac disease in breast cancer be mitigated with cardiac-sparing techniques? [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P1-10-13.