Imaging Efficacy of [18F]CTT1057 PET for the Detection of PSMA-Positive Tumors Using Histopathology as Standard of Truth: Results from the GuideView Phase 2/3 Prospective Multicenter Study

[18F]CTT1057 is a highly selective prostate-specific membrane antigen (PSMA)-targeted PET radiotracer for prostate cancer (PCa) detection. This prospective study (GuideView, NCT04838626) evaluates the imaging efficacy of [18F]CTT1057 PET to detect PSMA-positive lesions against histopathology in patients with newly diagnosed, untreated, high-risk PCa. Methods: Between September 7, 2021, and October 26, 2023, 201 patients planned for radical prostatectomy were screened and 195 patients were enrolled. Of these, 184 patients received a median of 355 MBq (range, 195-400 MBq) of [18F]CTT1057 and underwent PET/CT 90 min (±30 min) later. Three masked central independent readers evaluated the images. Coprimary endpoints were patient-level sensitivity (including primary tumor and pelvic lymph nodes) and region-level specificity (including pelvic lymph nodes only) for detection of PSMA-positive lesions, using histopathology as the standard of truth. The lower-bound 95% CI needed to surpass 50% for patient-level sensitivity and 70% for region-level specificity. Success was defined as at least 2 of 3 central readers meeting these criteria. Secondary endpoints included the patient-level and region-level positive predictive value and accuracy, region-level sensitivity, inter- and intrareader variability, detection rate of distant metastasis, pharmacokinetics, and safety and tolerability assessments. Results: Of the 184 patients who received [18F]CTT1057, 172 patients were evaluable for efficacy. Among these, a median of 19 lymph nodes (interquartile range, 13.0-28.5 lymph nodes) were dissected per patient. Both coprimary endpoints were met, with lower bounds of 95% CIs surpassing the success criteria for all 3 readers for both patient-level sensitivity (range, 86.8%-90.0%; lower-bound 95% CI, 80.7%-84.5%) and region-level specificity (97.1%; lower-bound 95% CI, 92.7%). Interreader variability Fleiss κ was 63.9%; intrareader reproducibility Cohen κ was 89.4%-100%. [18F]CTT1057 had a favorable safety profile. Conclusion: GuideView confirmed the imaging efficacy of [18F]CTT1057 for the detection of PSMA-positive lesions, with high patient-level sensitivity and region-level specificity. Substantial interreader variability and almost perfect intrareader reproducibility suggest that [18F]CTT1057 findings are robust and reliable. [18F]CTT1057 will contribute to expanding access to PSMA PET imaging to properly diagnose and treat patients with PCa.