The role of PSMA PET/CT imaging in restaging of prostate cancer patients with low prostate-specific antigen levels

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.

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.

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.

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.

Nuclear medicine communications. 2016 Jan 28 [Epub ahead of print]

Levent Kabasakal, Emre Demirci, Jamal Nematyazar, Re┼čit Akyel, Baresh Razavi, Meltem Ocak, Aslan Aygun, Can Obek, Ali R Kural

aDepartment of Nuclear Medicine, Cerrahpasa Medical Faculty bDepartment of Pharmaceutical Technology, Pharmacy Faculty cDepartment of Urology, Cerrahpasa Medical Faculty, Istanbul University dDepartment of Nuclear Medicine, Sisli Etfal Training and Research Hospital eDepartment of Urology, Acibadem University Medical Faculty, Istanbul, Turkey.