BIOS-04. IMPACT OF TREATMENT RESPONSE TO NEOADJUVANT CHEMOTHERAPY ON BRAIN METASTASIS PATTERNS AND BREAST CANCER PROGNOSIS

Abstract The impact of pathologic complete response (pCR) on brain metastases (BM) in breast cancer remains unclear. We retrospectively analyzed 1,244 early-stage breast cancer patients who underwent neoadjuvant chemotherapy followed by surgery. Clinical features, BM incidence, and survival outcomes were assessed, with gene expression profiles compared between BM samples from pCR and non-pCR patients. Propensity score matching was applied to adjust baseline differences. BM occurred in 4.2% of patients, most frequently in triple-negative breast cancer (TNBC, 6.9%). In TNBC, non-pCR patients had a significantly higher BM rate (9.2% vs. 3.3%, P = 0.026). pCR was associated with lower metastatic burden, higher craniotomy rates, and longer survival (42 vs. 4 months, P = 0.002). Differential gene expression showed RPL27A and CTLA4 upregulation in pCR cases and PLXND1 in non-pCR BM. pCR correlates with favorable BM outcomes in TNBC and may indicate distinct metastatic mechanisms, supporting the need for tailored surveillance and preventive strategies.