PURPOSE: Approximately 10% of prostate cancer (PCa) are prostate-specific membrane antigen (PSMA)-negative, leading to blind spots in PSMA-based diagnosis. This study aimed to identify a potential target for PSMA-negative PCa and preliminarily evaluate the feasibility of using radionuclide probe targeting the identified target for PCa diagnosis. METHODS: Quantitative protein analysis was performed on eight PSMA-negative PCa and eleven controls to identify a potential molecular target, followed by validation with an expanded cohort using immunohistochemistry. Sixteen participants underwent [ RESULTS: Quantitative protein analysis revealed CD13 as the most significantly upregulated membrane protein in PSMA-negative PCa. Expanded validation results indicated that CD13 positivity rates were 92.9% (13/14), 82.7% (105/127), 91.7% (11/12), and 70% (14/20) in PSMA-negative PCa, PSMA-positive PCa, ductal adenocarcinoma of the prostate (DAC), and intraductal carcinoma of the prostate (IDC-P), respectively. In PCa participants, the median [ CONCLUSION: CD13 was a potential target for PSMA-negative PCa and also showed high positivity rates in PSMA-positive PCa, DAC, and IDC-P. [