Correlative Biomarker Analysis of PSMA Expression on CTCs and PSMA Imaging in a Phase I Study of PSMA-Targeted Tubulysin Conjugate EC1169

While EC1169 showed limited activity, CTC and imaging analyses showed significant heterogeneity in PSMA expression on CTCs in patients with predominantly PSMA-positive lesions on SPECT. Our study highlights the importance of assessing both PSMA-based CTC and imaging assays in future validation trials.