Abstract P2-02-03: Efficacy and Safety of the Addition of Internal Mammary Irradiation to Standard Adjuvant Radiation in Early-Stage Breast Cancer: A Systematic Review and Meta-analysis
Authors: Korzets Yasmin , Levitas Dina , Grubstein Ahuva , Corn Ben W , Amir Eitan , Goldvaser Hadar 
Published: March 2023

Abstract
Background: Adjuvant regional nodal irradiation together with whole breast or chest wall irradiation is considered standard of care in most node positive early breast cancer. Existing data on adding internal mammary irradiation (IMNI) to the regional nodal fields are inconsistent. The objective of this study was to conduct a meta-analysis to explore the efficacy and safety of adding IMNI to adjuvant radiotherapy in early-stage, high risk breast cancer. Methods: A search of PubMed and EMBASE identified randomized trials that investigated the addition of IMNI to standard adjuvant radiation in early-stage breast cancer. Hazard ratios (HRs) and 95% confidence intervals (CI) were extracted for overall survival (OS), breast cancer specific survival (BCSS), disease-free survival (DFS) and distant-metastasis free survival (DMFS). The odds ratios (ORs) for regional and loco-regional recurrence, non-breast cancer mortality, secondary non-breast cancer, contralateral breast cancer and cardiovascular morbidity and mortality were also extracted. These data where pooled in a meta-analysis using RevMan 5.4. Results: Analysis included 5 trials comprising 10,994 patients. Compared to the control group, IMNI was associated with a small, but statistically significant improvement in OS (HR=0.91, 95% 0.85-0.97, p=0.004), BCSS (HR=0.84, 95%0.77-0.92, p&lt; 0.001), DFS (HR=0.89, 95% CI 0.82-0.98, p= 0.01) and DMFS (HR=0.89, 95% 0.81-0.98, p=0.02). IMNI was also associated with reduced odds for regional (OR=0.58, 95% 0.44-0.75, p&lt; 0.001) and loco-regional recurrence (OR=0.85, 95% CI 0.72-1.00, p=0.04). Subgroup analyses for OS by tumor location (medial/central vs. lateral) and by nodal burden showed similar benefit is all subgroups. The odds for cardiotoxicity were higher, but did not reach statistical significance (OR=1.23, 95% 0.99-1.53, p=0.07). There was no association with cardiovascular mortality (OR=1.00, 95% 0.69-1.46, p=1.00). There were also comparable odds for non-breast cancer mortality (OR=1.05, 95% 0.79-1.41, p=0.74), secondary cancer (OR=0.95, 95% 0.82-1.10, p=0.51) and contra-lateral breast cancer (OR=1.07, 95% 0.77-1.51, p=0.68). Conclusions: Compared to the control group the addition of IMNI in high-risk patients is associated with a statistically significant improvement in survival, albeit with a magnitude of questionable clinical meaningfulness. Non-significant association with increased cardiovascular toxicity requires further study in longer-term studies.
Citation Format: Yasmin Korzets, Dina Levitas, Ahuva Grubstein, Ben W Corn, Eitan Amir, Hadar Goldvaser. Efficacy and Safety of the Addition of Internal Mammary Irradiation to Standard Adjuvant Radiation in Early-Stage Breast Cancer: A Systematic Review and Meta-analysis [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-02-03.