In 2017, PSMA PET is able to detect >50% of PSMA positive lymph nodes with a short axis diameter <8mm. When comparing 18F-fluoromethylcholine and 68Ga-PSMA at various PSA levels, the head-to-head detection level at various cut-points favors 68Ga-PSMA: PSA <0.5 ng/mL – 50% vs 12.5%; PSA 0.5-2.0 ng/mL – 71% vs 36%; PSA >2.0 ng/mL – 88% vs 63% . However, as Dr. Haberkorn notes, even though 68Ga-PSMA PET outperforms conventional CT imaging for detection of lymph node metastases, what do we do when planning for IMRT regarding the lesions that we don’t see? Importantly, if 68Ga-PSMA PET increases detection of lesions, does it change treatment planning? In a small study assessing primary prostate cancer recurrences (n=44; n=15 initial diagnoses), 63% of patients had overall management changed after 68Ga-PSMA PET imaging .
The quest for improved PSMA radiotracers is ongoing. A new radiofluorinated molecule resembling the structure of therapeutic PSMA-617 has been developed in pre-clinical models, 18F-PSMA-1007. This radiotracer has no plasma binding and no metabolism in human plasma, as well as little radioactivity in the bladder and cleavage of the tracer in the kidneys . 18F-PSMA-1007 is now undergoing initial clinical validation in humans. Finally, Dr. Haberkorn’s group is at the cutting edge of PSMA therapeutics, concluding his presentation with impressive images of a patient with multiple bone metastases receiving 225-Actinium-PSMA (225-Ac-PSMA) and experiencing a complete durable radiographic/PSA response after three treatments of 225-Ac-PSMA.
Speaker: Uwe Haberkorn, University Hospital Heidelberg and DKFZ Heidelberg, Heidelberg, Germany
Written By: Zachary Klaassen, MD, Urologic Oncology Fellow, University of Toronto, Princess Margaret Cancer Centre, Twitter: @zklaassen_md at the European Society for Medical Oncology Annual Congress - September 8 - 12, 2017 - Madrid, Spain
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2. Cardinale J, Schafer M, Benesova M, et al. Preclinical evaluation of 18F-PSMA-1007, a new prostate-specific membrane antigen ligand for prostate cancer imaging. J Nucl Med 2017;58(3):425-431.