Abstract: Background and purpose: Prostate-specific membrane antigen (PSMA), a cell surface protein with high expression in prostate carcinoma (PC) cells, is an attractive target for PC imaging and therapy. Small-molecule radiopharmaceuticals targeting PSMA can detect the location and extent of disease with high sensitivity and specificity. The aim of this study was to evaluate the value of technetium-99m-labelled small molecule against PSMA (HYNICGlu- Urea-A, ^99mTc-PSMA) for the detection of primary and metastatic prostate cancers. Methods: Twenty-four prostate cancer patients and 1 patient with benign prostate hyperplasia received whole-body scan followed by abdominopelvic SPECT/CT 2 h after intravenous injection of ^99mTc-PSMA. Tumor to muscle uptake ratio of ^99mTc-PSMA was calculated using region of interest (ROI) technology. The sensitivity and specificity of ^99mTc-PSMA were evaluated. The relationships between positive ^99mTc-PSMA and prostate specific antigen (PSA) level and Gleason Score were analyzed. Results: Based on per patient, the sensitivity and specificity of ^99mTc-PSMA were 72.7% (16/22) and 100% (3/3), respectively. The level of PSA in patients with positive ^99mTc-PSMA imaging was significantly higher than that in patients with negative ^99mTc-PSMA imaging [(PSA median 17.31 ng/mL, range: 2.26-3 239.0 ng/mL) vs (PSA median 0.49 ng/ mL, range: 0.07-9.28 ng/mL)] (Z=-3.51, P<0.001). Among newly diagnosed patients and recurrent patients with PSA more than 2.0 nm/mL, it was apparent that ^99mTc-PSMA imaging was able to detect lesions with improved sensitivity of 94.1% (16/17). Gleason Scores between positive ^99mTc-PSMA patients and negative ^99mTc-PSMA patients were not significantly different (Z=-0.69, P=0.52). Conclusion: With the combination of whole-body scan and tomography, ^99mTc-PSMA SPECT/CT can be an excellent and specific molecular imaging strategy to detect prostate cancer and its metastases.

Key words: Prostate cancer, Prostate-specific membrane antigen, Prostate-specific antigen, Gleason Score, ^99mTc-PSMA imaging