Abstract PS4-10-08: Impact of BRCA Mutation Status on Pathologic Complete Response and Treatment Patterns in Triple-Negative Breast Cancer Patients Treated with Chemoimmunotherapy: A Real-World Analysis

Abstract Background Pathologic complete response (pCR) following neoadjuvant chemoimmunotherapy is an important prognostic marker in triple-negative breast cancer (TNBC). BRCA mutation carriers may exhibit distinct clinical features and treatment responses. We aimed to assess the impact of BRCA status on pCR and treatment patterns among TNBC patients receiving KN522 neoadjuvant regimens in a real-world setting. Methods We identified 45 BRCA-tested patients with stage I-III TNBC who received a KN522 chemoimmunotherapy regimen at King Fahad Medical City between January 2021 and December 2022. Clinicopathologic characteristics, treatment compliance, surgical approach, and pCR (defined as ypT0/is ypN0) were compared between BRCA-positive and BRCA-negative groups. Results Of the 45 patients, 11 (24.4%) were BRCA-positive and 34 (75.6%) were BRCA-negative. BRCA-positive patients were younger (median age 38 vs 46 years) and more likely to have bilateral breast cancer (9.1% vs 2.9%). Grade 3 tumors predominated in both groups (91%), and mastectomy was more frequent among BRCA-positive patients (81.8% vs 64.5%). The pCR rate was 81.8% in BRCA-positive patients (9/11) compared to 48.4% in BRCA-negative patients (15/31), showing a trend toward statistical significance (p = 0.08). Treatment compliance was high: 63.6% of BRCA-positive and 70.6% of BRCA-negative patients completed the full planned regimen. Early discontinuation occurred in 18.2% and 26.5% of patients, respectively. Adjuvant PARP inhibitors were given to 2 BRCA-positive patients (18.2%), while 8 BRCA-negative patients (23.5%) received adjuvant capecitabine. Conclusion In this real-world cohort of TNBC patients treated with neoadjuvant chemoimmunotherapy, BRCA-positive patients demonstrated a higher pCR rate and distinct clinicopathologic characteristics, including younger age and higher mastectomy rate. Treatment compliance and tolerability were acceptable across groups. These findings support the potential role of BRCA status in guiding neoadjuvant strategies in early-stage TNBC. Citation Format: M. F. ALDAWOUD, F. T. FAQIHI, N. ALGAZLAN, M. M. ALHARBI, A. A. ALMAZYAD, A. R. ALTAMIMI, M. RUDAINEE, A. A. ALWOHAIBI, A. K. ALTWAIRGI. Impact of BRCA Mutation Status on Pathologic Complete Response and Treatment Patterns in Triple-Negative Breast Cancer Patients Treated with Chemoimmunotherapy: A Real-World Analysis [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 PS4-10-08.