2929 - Evaluating the Impact of Adjuvant Radiation Therapy on Survival in Early Stage HER2-Positive Invasive Breast Carcinoma Following Breast-Conserving Surgery

Purpose/Objective(s): The role of adjuvant radiation therapy (RT) following breast-conserving surgery (BCS) with chemotherapy in patients with early stage HER2-positive invasive breast cancer remains uncertain. This retrospective study hypothesizes that RT improves overall survival in this population, aiming to inform clinical decision-making and complement ongoing prospective trials, such as the HERO trial, which evaluates radiotherapy optimization for low-risk HER2-positive breast cancer.

Materials/Methods: Using the National Cancer Database (2004–2021), 7,961 patients were analyzed who met HERO trial-aligned inclusion criteria: male and female patients who underwent BCS with adjuvant chemotherapy, age = 40 years, histologically confirmed invasive breast carcinoma, HER2-positive, ER and PgR status assessed, axillary staging performed with all examined nodes negative, and pT1N0M0 staging. Patients were stratified by RT status (adjuvant RT vs. no RT received). Kaplan-Meier survival analysis with log-rank testing was performed to compare overall survival between the two groups. A Cox proportional hazards model evaluated the independent impact of RT adjusted for age and comorbidity burden as measured by the Charlson-Deyo Comorbidity Index.

Results: A total of 7,961 patients met the inclusion criteria, with 7,478 patients having received adjuvant RT and 483 who had no RT. RT conferred a 7.3-month improvement in median overall survival (78.6 vs. 71.3 months, log-rank p<0.0001) and a 17.3% absolute increase in median survival rate (95.1% vs. 77.8%). Multivariate Cox regression analysis demonstrated significant survival advantage for the RT cohort, with a 73% reduction in mortality risk (hazard ratio = 0.270, 95% CI: 0.216–0.337, p<0.0001) after adjusting for age and comorbidity burden.

Conclusion: These findings suggest that adjuvant radiation therapy is associated with clinically meaningful improvement in survival outcomes in early stage (T1N0) HER2-positive breast cancer patients treated with BCS and chemotherapy. While radiation therapy provides a survival benefit, further research (e.g., HERO prospective randomized trial) is needed to refine patient selection criteria and identify those who may safely omit radiation without compromising outcomes.