Patient-Derived Organoids to Functionally Characterize Chemotherapy Resistance in Breast Cancer

This prospective observational study aims to functionally characterize chemotherapy resistance in patients with locally advanced breast cancer undergoing neoadjuvant chemotherapy. Despite standard molecular classification, significant heterogeneity in treatment response exists, and the biological mechanisms underlying chemoresistance remain incompletely understood. In this study, patient-derived organoid (PDO) models will be established from tumor tissues obtained during routine clinical care. These three-dimensional models preserve the biological characteristics of individual tumors and enable ex vivo functional assessment of drug response. Chemotherapy sensitivity and resistance will be evaluated using quantitative parameters including Half-Maximal Inhibitory Concentration (IC50) values, cell viability, and apoptotic response. Functional data obtained from PDO models will be correlated with clinical and pathological treatment outcomes, particularly pathological complete response (pCR), to assess the predictive value of PDO-based assays. In addition, apoptotic biomarkers such as Caspase-3/7 will be measured in serum samples collected during routine clinical evaluation and analyzed in relation to treatment response. Furthermore, selected Food and Drug Administration (FDA) and European Medicines Agency (EMA) approved small molecules will be tested in PDO models to evaluate their potential to reverse chemotherapy resistance, supporting drug repurposing strategies. This study aims to establish a functional, patient-specific platform for assessing chemoresistance and to contribute to the development of personalized therapeutic approaches in breast cancer.