RT Journal Article SR Electronic T1 The Role of Castrate Status and Androgen Deprivation Therapy in PSMA-Based 18F-DCFPyL PET/CT Imaging of Metastatic Prostate Cancer Patients. JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 1357 OP 1357 VO 62 IS supplement 1 A1 Mena, Esther A1 Lindenberg, Maria Liza A1 Turkbey, Ismail A1 Lin, Frank A1 Ton, Anita A1 Eclarinal, Philip A1 Adler, Stephen A1 McKinney, Yolanda A1 Weaver, Juanita A1 Dahut, William A1 Choyke, Peter YR 2021 UL http://jnm.snmjournals.org/content/62/supplement_1/1357.abstract AB 1357Objectives: To investigate the performance of 18F-DCFPyL, a Prostate-Specific Membrane Antigen (PSMA) targeted PET agent, in a prospective cohort of patients with documented metastatic prostate cancer (Pca) with androgen deprivation therapy (ADT). The performance of 18F-DCFPyL may depend on patients’ castrate status and time to hormone treatment exposure. Methods: This is a prospective IRB-approved, single-institution study, including 37 patients (median age 69 years-old, median PSA: 6.3 ng/mL; range 0.02-5000 ng/mL). Fourteen patients were metastatic castrate-sensitive Pca (CSPC) and 23 castrate-resistant Pca (CRPC). All patients had prior exposure to ADT and 32 of them were on ADT at the time of the scan. Patients underwent whole-body 18F-DCFPyL-PET/CT at 2 h post-injection (299.9±15.5 MBq). Lesion detection, tumor PSMA-PET standard uptake value (SUV), PSMA-derived tumor volume burden, total lesion PSMA and duration of ADT were assessed and compared between cohorts. Correlations between PET-PSMA parameters and PSA values were also evaluated. Results: 18F-DCFPyL-PET scan detected metastatic disease in all patients, identifying significantly more number of lesions in CRPC patients than in CSPC (15± 77.9 vs 4.0±6.7 lesions, p<0.001) and higher tumor volume burden (36.6±1074 ml vs 19.3±33.2 ml, p<0.05). Tumor PSMA-PET SUVmax was significantly higher in CRPC than in CSPC patients with median SUVmax of 46.9±42.0 vs 20.2±16.4, p=0.002. Total lesion PSMA was higher for CRPC compared to CSPC patients (305.3±5230 vs 59.07±362.1 vs, p<0.05). PSA at the time of scan correlated with total tumor volume burden (r=0.48, p=0.002) for all patients, and with the tumor uptake (SUVmax) for CSPC patients (r=0.66, p=0.007) but not for CRPC patients. The median duration of ADT was 25.4 months, ranging from 1 to 87 months. In patients on ADT at the time of the scan (n=32), the PSMA uptake was lower for early castrate-sensitive patients on short-term ADT (when PSA was below 2 ng/mL) compared to those with advanced disease and long-term ADT (p< 0.05). Patient accrual is ongoing for this trial and more results will be available at the time of presentation. Conclusions: 18F-DCFPyL-PET imaging was able to identify metastatic lesions in patients with castrate-sensitive and castrate-resistant metastatic Pca. In advanced mCRPC, 18F-DCFPyL-PET/CT demonstrated more lesions, with higher tumor volume burden, and higher PSMA-PET uptake than in CSPC patients. For early CSPC patients on short-term ADT (PSA <2 ng/mL), the PSMA uptake was lower than for patients on long-term ADT. The utility of PSMA-targeting imaging in metastatic prostate cancer appears to depend on patient’s castrate status and ADT exposure time.