The role of 68Ga-PSMA PET/CT scan in biochemical recurrence after primary treatment for prostate cancer : a systematic review of literature

Introduction: Recurrence after primary treatment of prostate cancer is one of the major challenges facing urologists. Biochemical recurrence is not rare and occurs in up to one third of the patients undergoing radical prostatectomy. Management of biochemical recurrence is tailored according to the site and the burden of recurrence. Therefore, developing an imaging technique to early detect recurrent lesions represents an urgent need. Positron emission tomography (PET) of 68Ga-labelled prostate-specific membrane antigen (68Ga-PSMA) is an emerging imaging modality that seems to be a promising tool with capability to localize recurrent prostate cancer. A systematic review of literature was done to evaluate the role of 68Ga-PSMA PET/CT scan in patients with recurrent prostate cancer after primary radical treatment. Evidence acquisition: A systematic and comprehensive review of literature was performed in September 2017 analyzing the MEDLINE and Cochrane Library following the Preferred Reporting Items for Systematic Review and Meta-analysis (PRISMA) statement. The following key terms were used for the search "PSMA," "prostate-specific membrane antigen," "positron emission tomography," "PET," "recurrent," "prostate cancer," "prostate neoplasm," "prostate malignancy," and "68Ga." Risk of bias was assessed using the Quality Assessment of Diagnostic Accuracy Studies-2 tool. Evidence synthesis: Thirty-seven articles met our inclusion criteria and were included in the analysis of this systematic review. Of the 37 articles selected for analysis only four studies were prospective. The overall detection rate of 68Ga-PSMA PET scan ranged from 47% up to 96.6%. The main advantage of this imaging technique is its relatively high detection rates at low serum PSA levels below 0.5 ng/mL (ranging from 11.1% to 75%). Higher serum PSA level was strongly associated with increased positivity on 68Ga-PSMA PET scan. 68Ga-PSMA PET scan was found superior to conventional imaging techniques (CT and MRI) in this setting of patients and even it seems to outperform choline-based PET scan. This technique provided significant changes in the therapeutic management of 28.6-87.1% of patients. Conclusions: After biochemical recurrence, the primary goal is to locate the recurrent lesions' site. 68Ga-PSMA PET/CT seems to be effective in identifying recurrence localization also for very low levels of PSA (<0.5 ng/mL) thus permitting to choose the best therapeutic strategy as early as possible. However, data available cannot be considered exhaustive and prospective randomized trials are needed.