Pathological complete response and oncological outcomes in locally advanced breast cancers treated with neoadjuvant radiotherapy: an Australian perspective.

BACKGROUND AND PURPOSE: To assess the degree of pathological complete response (pCR), post-operative surgical complication rates and oncological outcomes in women with locally advanced (LABC) or high-risk breast cancers treated with neoadjuvant radiotherapy (NART).

MATERIALS AND METHODS: This retrospective multi-institutional review involved 138 clinically-staged patients with 140 breast cancers treated with NART between January 2014 and February 2021. Treatments involved sequential NACT and NART, followed by mastectomy with or without axillary surgery and immediate autologous breast reconstruction. Descriptive statistics were used to assess patient and disease features, treatment regimens, pathological response and factors affecting post-operative complications. Kaplan-Meier curves were performed to assess locoregional recurrence free, distant metastasis free and overall survival outcomes.

RESULTS: Median age was 47 years (IQR 42-52). The median follow-up was 35.2 months (IQR 17.1-46.5). pCR was achieved in 36.4% (as defined by Chevallier Classification) or 42.1% (as defined by Miller-Payne scores) of patients. Higher pCR rates were achieved for HER2 positive (73.8%-85.7%) and triple negative phenotypes (47.6%-57.1%). There were 21 Grade 3 surgical complications including 10 Grade 3B breast events and 8 grade 3B donor-site events, where surgical reintervention was required. At 3-years follow-up, the locoregional recurrence free survival was 98.1%, distant metastasis free survival was 83.6% and overall survival was 95.3%%.

CONCLUSION: NART is feasible to facilitate a single-stage mastectomy and immediate autologous breast reconstruction. This study demonstrated comparable rates of post-operative complication to standard of care, and high rates of pCR which translates to high rates of locoregional control, distant metastasis free survival and overall survival.