Abstract 2671: TROP2 expression predicts sensitivity to datopotamab deruxtecan (Dato-DXd) in patient-derived breast cancer organoids

Abstract Background: Trophoblast cell surface antigen 2 (TROP2) is a transmembrane glycoprotein preferentially expressed in many cancers relative to normal tissues. TROP2 has recently emerged as a promising therapeutic target in breast cancer, leading to the development of TROP2-directed antibody-drug conjugates (ADCs), including datopotamab deruxtecan (Dato-DXd). However, mechanisms underlying heterogeneous responses to Dato-DXd remain poorly defined. In this study, we evaluated the effect of Dato-DXd on the breast cancer patient-derived organoids (PDOs) and analyzed their responses in correlation with the TROP2 H-score of PDOs. Method: TROP2 expression and Dato-DXd sensitivity were evaluated by western blot analysis in breast cancer cell lines representing different subtypes. The TROP2 band intensity on western blot was quantified across the cell lines to determine TROP2 expression. We obtained surgical or biopsy specimens from patients with breast cancer at Yonsei Cancer Center. PDOs were established and subjected to TROP2 immunohistochemistry (IHC). TROP2 H-scores were quantified using ImageJ IHC Profiler. PDO cell viability following ADC exposure was assessed using the CellTiter-Glo 3D assay. Results: We evaluated TROP2 expression in a series of breast cancer cell lines. High TROP2 expression was observed in MDA-MB-468 and HCC1937 (triple-negative breast cancer [TNBC]), T-47D (HR+/HER2-), and SK-BR-3 (HER2+). The sensitivity to Dato-DXd in IC50 value was well correlated with the TROP2 protein expression, suggesting TROP2 expression level is an important determinant of Dato-DXd response. In particular, SK-BR3 showed both response to Dato-DXd and T-DXd in line with its high TROP2 and HER2 expression, whereas BT474 showed only response to T-DXd, but not to Dato-DXd. We next evaluated TROP2 expression in PDOs of patients with breast cancer (n=34) and the median TROP2 H-score was 152. The PDOs of high TROP2 expression (H-score ≥ 100, n= 28) exhibited significantly greater sensitivity to Dato-DXd compared to TROP2-low PDOs (H-score < 100, n= 6). Importantly, Dato-DXd showed potent antitumor activity in three treatment-refractory TNBC PDOs, including models derived from tumors progressing after pembrolizumab plus chemotherapy combination (IC50: OSV-001, 0.82 nM; SBO-105, 0.27 nM) and sacituzumab govitecan (IC50: OSV-011, 0.55nM), whereas T-DXd showed lower activity compared to Dato-DXd in these organoids (IC50: OSV-001, 200 nM; SBO-105 = 160 nM; OSV-011, not reached). Conclusion: These findings demonstrate that TROP2 expression is a key determinant of Dato-DXd sensitivity and provide mechanistic insights into ADC resistance. Our results support the potential of TROP2-guided patient stratification to enhance therapeutic outcomes with Dato-DXd in breast cancer. Dato-DXd showed significant antitumor activity in PDOs from tumors resistant to anti-PD-1 and ADC treatment. Citation Format: Won-Ji Ryu, Min Hwan Kim, Geon-Uk Kim Kim, Joohyuk Sohn, Yumi Hwang, Jeong Dong Lee, Shinyoung Park, Hyun Myoung Yun, Kyoo Hyun Kim, Gun Min Kim, Hyung Seok Park. TROP2 expression predicts sensitivity to datopotamab deruxtecan (Dato-DXd) in patient-derived breast cancer organoids [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 2671.