New PSMA PET tracer aids detection of prostate cancer recurrence
Dr Brett Sounness, South Coast Radiology and GCUH
Modern treatment strategies have significantly improved progression-free survival of patients with prostate cancer (PCa). However early detection of recurrent disease location after prostatectomy or radiotherapy still remains challenging. Until now, observing early metastatic spread to lymph nodes and bone has not been possible. A new PET molecular imaging technique using prostate-specific membrane antigen (PSMA) has demonstrated excellent sensitivity in detection of low volume metastatic PCa. If this small volume disease is accessible for surgery or radiation therapy, patients may be cleared of disease in the short term and systemic therapy and the resultant side effects can be delayed. As such the ability to visualise these early metastatic deposits and early PCa recurrence is very relevant for staging, prognosis, and planning therapies to optimise patient outcomes.
PSMA is a cell surface target that is highly expressed by nearly all prostate cancers with enhanced expression levels found in poorly differentiated, aggressive tumours, metastatic and hormone-refractory carcinomas. Due to the high PSMA uptake in PCa cells it is an ideal biological target for PET imaging of PCa, especially for visualising small lymph node, bone and liver metastases. The ability to identify and localise PCa recurrence in patients with elevated serum (PSA) but with no other symptoms after definitive therapy, is the goal of PSMA PET-CT.
In a recent publication in the European Journal of Nuclear Medicine and Molecular Imaging, Dr Afshar-Oromieh and colleagues demonstrated that PSMA PET-CT identified a large number of positive findings in the clinically important range of low PSA values (less than 0.5 ng/mL). Their study evaluated 319 patients, most of whom were suspected to have progressive disease following prior conventional PCa treatment (radiation therapy and/or surgery). All were given contrast-enhanced PET-CT after injection of Gallium-68-PSMA. A lesion-based analysis revealed values of 77% sensitivity, 100% specificity, 91.4% NPV and 100% PPV. They concluded that the distinct advantage of PSMA PET CT is the ability to observe high PSMA uptake at the sites of involved lymph nodes, whether or not they are enlarged. If assessment was made on CT alone, these nodes may not be identified as metastatic on size criteria.
South Coast Radiology is the first PET facility on the Gold Coast to offer Gallium 68 labelled PSMA PET imaging. The radioisotope is produced on site using a fully automated radiopharmaceutical synthesis device. Currently there is no Medicare funding for this scan and SCR is providing the service at a cost of $600, with the CT component of the imaging bulk-billed.
Various authors have concluded that PSMA PET-CT can detect small PCa recurrent or metastatic lesions with significantly improved sensitivity when compared to all other medical imaging examinations. This will increase early detection hopefully leading to successful short term treatment of the disease provided by our Urology and Radiation Oncology colleagues. As we have in place for the multi-parametric MRI scan, we feel that either Radiation, Medical Oncology or Urology review prior to PSMA PET-CT will ensure best utilisation of the technique. Please feel free to contact myself or SCR PET radiologists, Drs Sally Sojan, Adam Tonakie and Ash Walton for further information on this exciting new technology.
- Afshar-Oromieh, et al. Comparison of PET imaging with a 68Ga-labelled PSMA ligand and 18F-choline-based PET/CT for the diagnosis of recurrent prostate cancer. European Journal of Nuclear Medicine and Molecular Imaging. 2014
- Schäfer M, et al. A dimerized urea-based inhibitor of the prostate-specific membrane antigen for 68Ga-PET imaging of prostate cancer. EJNMMI Research. 2012
- Eder M, et al. Novel Preclinical and Radiopharmaceutical Aspects of [68Ga]Ga-PSMA-HBED-CC: A New PET Tracer for Imaging of Prostate Cancer. Pharmaceuticals. 2014
- Eder M et al. Detection rate for a novel 68Ga-PSMA PET-ligand in patients with biochemical recurrence of prostate cancer using PET-CT and PET-MR imaging. J Nucl Med. 2014; 55 (Supplement 1)
- Afshar-Oromieh A, et al. The diagnostic value of PET/CT imaging with the 68Ga-labelled PSMA ligand HBED-CC in the diagnosis of recurrent prostate cancer. European Journal of Nuclear Medicine and Molecular Imaging. 2015.