Abstract PS5-05-12: Real-world outcomes of neoadjuvant therapy for breast cancer: a regional australian cohort study

Abstract Background Neoadjuvant therapy is increasingly utilised in early and locally advanced breast cancer to improve operability and provide an early in vivo assessment of treatment response. Achieving pathological complete response (pCR) is associated with improved long-term outcomes, particularly in HER2-positive and triple-negative breast cancer (TNBC). While major trials have reported neoadjuvant therapy outcomes by tumour subtype, real-world data from regional centres remain limited. This study evaluates pCR rates, treatment completion, and treatment-related toxicities in a regional Australian cohort receiving neoadjuvant therapy for breast cancer. Methods A retrospective audit was conducted of all female patients with early or locally advanced breast cancer who received neoadjuvant systemic therapy followed by surgery at Goulburn Valley Health, Victoria, between January 2020 and May 2025. Data collected included demographics, tumour subtype, treatment details, hospitalisations during therapy, and rate of pathological complete response. Results 70 patients underwent neoadjuvant therapy at Goulburn Valley Health. Subtypes included HER2-positive (n=28), triple-negative breast cancer (TNBC; n=26), and hormone receptor-positive/HER2-negative (HR+/HER2−; n=16). 47 patients (67.1%) completed their planned neoadjuvant therapy. 21 patients (30%) required hospital admission during their neoadjuvant therapy. Surgical procedures after therapy included breast-conserving surgery in 36 patients, single mastectomy in 25, and bilateral mastectomy in 8 patients. 1 TNBC patient did not proceed to surgery due to disease progression. Pathologic complete response (pCR) rates were 42.9% (12/28) in HER2-positive, 38.5% (10/26) in TNBC, and 6.3% (1/16) in HR+/HER2− patients. Notable differences in pCR rates were observed between patients who completed neoadjuvant therapy and those who did not. In the HER2-positive group, 57.1% (12/21) of patients who completed therapy achieved pCR, compared to 0% (0/7) among non-completers. In the TNBC group, pCR was achieved in 50% (8/16) of patients who completed therapy versus 20% (2/10) of patients who did not. Conclusion This regional Australian cohort demonstrates pCR rates comparable to published literature, with a higher pCR rate seen in HER2+ and TNBC subtypes versus HR+/HER2−. Completion of the planned neoadjuvant therapy regimen was associated with increased pCR rates in both TNBC and HER2-positive subgroups. These findings highlight the importance of supportive care to minimise treatment interruptions, aiding in neoadjuvant therapy completion. Citation Format: D. Bu, J. Torres, A. Sahu. Real-world outcomes of neoadjuvant therapy for breast cancer: a regional australian cohort study abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS5-05-12.