Clinical efficacy of tumor organoid‐guided cancer therapy for locally advanced unresectable or metastatic breast cancer

Abstract Patient‐derived organoids (PDOs) may facilitate treatment selection. This retrospective cohort study evaluated the feasibility and clinical benefit of using PDOs to guide personalized treatment in metastatic breast cancer (MBC). Patients diagnosed with MBC were recruited between January 2019 and August 2022. PDOs were established and the efficacy of customized drug panels was determined by measuring cell mortality after drug exposure. Patients receiving organoid‐guided treatment (OGT) were matched 1:2 by nearest neighbor propensity scores with patients receiving treatment of physician's choice (TPC). The primary outcome was progression‐free survival. Secondary outcomes included objective response rate and disease control rate. Targeted gene sequencing and pathway enrichment analysis were performed. Forty‐six PDOs (46 of 51, 90.2%) were generated from 45 MBC patients. PDO drug screening showed an accuracy of 78.4% (95% CI 64.9%–91.9%) in predicting clinical responses. Thirty‐six OGT patients were matched to 69 TPC patients. OGT was associated with prolonged median progression‐free survival (11.0 months vs. 5.0 months; hazard ratio 0.53 [95% CI 0.33–0.85]; p = .01) and improved disease control (88.9% vs. 63.8%; odd ratio 4.26 [1.44–18.62]) compared with TPC. The objective response rate of both groups was similar. Pathway enrichment analysis in hormone receptor‐positive, human epidermal growth factor receptor 2‐negative patients demonstrated differentially modulated pathways implicated in DNA repair and transcriptional regulation in those with reduced response to capecitabine/gemcitabine, and pathways associated with cell cycle regulation in those with reduced response to palbociclib. Our study shows that PDO‐based functional precision medicine is a feasible and effective strategy for MBC treatment optimization and customization.