Introduction: Prostate-specific membrane antigen (PSMA) is increasingly being recognized as a novel target for the PET imaging of prostate cancer (PCa) and Ga-DKFZ-11 (Ga-PSMA) has been suggested as a novel tracer for detection of PCa relapses and metastases. The aim of this study was to evaluate the diagnostic value of PSMA PET/CT in the diagnosis of recurrent PCa with low prostate-specific antigen (PSA) levels.
Patients and methods: We carried out a retrospective analysis of patients who underwent PSMA PET/CT from November 2013 to December 2014 in our department. Among these patients, 50 out of 178 who had increasing PSA levels (<5 ng/ml) and did not have known metastasis were included in this study.
Results: Patients had an average PSA of 1.41 ng/ml. A total of 29 patients (58%) showed at least one positive lesion. PET positivity rates of 31% (n=4), 54% (n=13), and 88% (n=14) were observed in patients with a PSA level of less than 0.2, 0.2-2, and 2-5 ng/ml, respectively. A positive correlation was observed between positivity rate and Gleason scores and blood PSA levels. Verification was performed in 46 patients, with biopsy (n=3) and follow-up, and conventional imaging studies at the time of the PET/CT or during follow-up with a mean period of 10.6±3.3 months and ranged from 3.8 to 16.4 months. According to patient-based analysis of 46 cases, 57% of patients had true positive, 24% of patients had true negative, 2% of patients had false positive, an 18% of patients had false-negative findings. A sensitivity of 76.47% (95% confidence interval: 58.83-89.25%) and a specificity of 91.67% (95% confidence interval: 61.52-99.79%) were found.
Conclusion: PET/CT with Ga-PSMA is a valuable tool for assessing recurrence of PCa with a high sensitivity in patients who have PSA levels between 0.2 and 5 ng/ml. In addition, this study suggests that PSMA PET/CT can be used in patients with very low (<0.2 ng/ml) but increasing PSA levels, which, in many cases, may influence further clinical management.