San Antonio, Texas USA (UroToday.com) In this session Dr. Twardowski discussed the role of various imaging modalities in detecting metastatic prostate cancer. Historically, a PSA level of > 0.2ng/mL post-prostatectomy has been used as an indication of recurrence, and the success of salvage therapy is approximately 50% in this setting. Thus, roughly half of men with PSA > 0.2ng/mL after prostatectomy harbor occult metastatic disease that traditional imaging modalities (e.g. computed tomography scan and bone scan) are unable to detect.
Dr. Twardowski focused his discussion on magnetic resonance imaging (MRI) and positron emission tomography (PET). Diffusion-weighted MRI techniques can identify 10-15% of metastatic prostate cancer over computed tomography (CT) scan and bone scan, and it has the advantage of not requiring gadolinium contrast agents. Thus, there is growing support for MRI in the detection of metastatic disease in these patients.
Most of the growth in detection of occult metastatic disease is occurring in the context of PET scanning. PET scans use prostate cancer avid molecules such as choline, fluciclovine, and prostate-specific membrane antigen (PSMA) analogues linked to a positron emitting tracer.
Fluorodeoxyglucose (FDG) PET does not work well in prostate cancer due its low glucose metabolizing nature. Sodium fluoride PET is very sensitive and results in approximately a 16.2% improvement over bone scan and CT scan, but has a low specificity with many false positives. Choline PET is based on choline kinase expression in prostate cancer. The major limitation to this approach is its modest performance at low prostate specific antigen (PSA) levels. Fluciclovine PET was recently FDA-approved. It is slightly superior to choline PET, but its effectiveness in identifying metastatic disease is also limited at low PSA levels. Lastly, PSMA-based PET is gaining traction in Europe and is available in some clinical trials in the United States. It has improved performance characteristics at lower PSA levels identifying greater than 50% of metastatic lesions at PSA levels < 0.5ng/mL.
In conclusion, new imaging modalities are more sensitive in visualizing metastatic prostate cancer than traditional CT and bone scan. Whether these new scans improve clinical outcomes is an area of active investigation. From a practical standpoint in 2016 in the United States, Dr. Twardowski recommends diffusion-weighted MRI of the spine and pelvis combined with 18F-fluciclovine PET/CT for patients with a rising PSA after primary therapy. While PSMA-based PET is exciting, its availability is currently restricted to clinical trials in the United States. Finally, Dr. Twardowski encouraged the development of clinical trials to assess the outcomes of salvage therapy based on guidance from these new imaging modalities.
Presented By: Przemyslaw W. Twardowski, MD
Written By: Benjamin T. Ristau, MD, Society of Urologic Oncology Fellow, Fox Chase Cancer Center
17th Annual Meeting of the Society of Urologic Oncology - November 30 -December 2, 2016 – San Antonio, Texas USA