TY - JOUR T1 - Imaging Patients with Metastatic Castration-Resistant Prostate Cancer Using <sup>89</sup>Zr-DFO-MSTP2109A Anti-STEAP1 Antibody JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 1517 LP - 1523 DO - 10.2967/jnumed.118.222844 VL - 60 IS - 11 AU - Jorge A. Carrasquillo AU - Bernard M. Fine AU - Neeta Pandit-Taskar AU - Steven M. Larson AU - Stephen E. Fleming AU - Josef J. Fox AU - Sarah M. Cheal AU - Joseph A. O’Donoghue AU - Shutian Ruan AU - Govind Ragupathi AU - Serge K. Lyashchenko AU - John L. Humm AU - Howard I. Scher AU - Mithat Gönen AU - Simon P. Williams AU - Daniel C. Danila AU - Michael J. Morris Y1 - 2019/11/01 UR - http://jnm.snmjournals.org/content/60/11/1517.abstract N2 - Six-transmembrane epithelial antigen of prostate-1 (STEAP1) is a relatively newly identified target in prostate cancer. We evaluated the ability of PET/CT with 89Zr-DFO-MSTP2109A, an antibody that recognizes STEAP1, to detect lesions in patients with metastatic castration-resistant prostate cancer (mCRPC). Methods: Nineteen mCRPC patients were prospectively imaged using approximately 185 MBq/10 mg of 89Zr-DFO-MSTP2109A. 89Zr-DFO-MSTP2109A PET/CT images obtained 4–7 d after injection were compared with bone and CT scans. Uptake in lesions was measured. Fifteen patients were treated with an antibody–drug conjugate (ADC) based on MSTP2109A; ADC treatment–related data were correlated with tumor uptake by PET imaging. Bone or soft-tissue biopsy samples were evaluated. Results: No significant toxicity occurred. Excellent uptake was observed in bone and soft-tissue disease. Median SUVmax was 20.6 in bone and 16.8 in soft tissue. Sixteen of 17 lesions biopsied were positive on 89Zr-DFO-MSTP2109A, and all sites were histologically positive (1 on repeat biopsy). Bayesian analysis resulted in a best estimate of 86% of histologically positive lesions being true-positive on imaging (95% confidence interval, 75%–100%). There was no correlation between SUVmax tumor uptake and STEAP1 immunohistochemistry, survival after ADC treatment, number of ADC treatment cycles, or change in prostate-specific antigen level. Conclusion: 89Zr-DFO-MSTP2109A is well tolerated and shows localization in mCRPC sites in bone and soft tissue. Given the high SUV in tumor and localization of a large number of lesions, this reagent warrants further exploration as a companion diagnostic in patients undergoing STEAP1-directed therapy. ER -