When imaging prostate cancer tumours, accuracy and sensitivity is essential for planning the most effective treatment. Increasingly clinicians are using an imaging modality called PSMA PET/CT to localize prostate cancer tumours. The ‘target’ for these scans is prostate-specific membrane antigen (PSMA), a protein found on the surface of prostate cancer cells. PSMA PET/CT scans are relatively new and appear to be more accurate and sensitive than older ways for localizing tumours.
A recent study examined the effects of ADT on the detection of tumours using a PSMA PET/CT agent called 68Ga-PSMA-11. Ten patients were scanned twice with PET/CT using 68Ga-PSMA-11. The patients started on ADT after the first scan and and continued on it to the second scan; the scans were separated on average by seven and a half months.
Findings: On the second scan many previously located tumours were no longer visible with PSMA PET/CT imaging when the men received ADT for 42 days or more. The researchers noted that the tumours were likely still present, but were no longer detectable with PSMA PET/CT scans.
Why this is important: Good imaging helps clinicians to understand the nature and location of the disease, and to make informed decisions about planning treatments. If ADT causes tumours to be less visible with PSMA PET/CT scans, this could interfere with effective treatment planning.
The researchers suggest that PSMA PET/CT scans should be done prior to starting ADT, to allow for the maximum visibility of tumours. However, for patients who are already on ADT, PSMA PET/CT scans may still be useful, particular if combined with PSA testing. As the researchers note, “early detection of hormone-resistant lesions could change the treatment strategy.”
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Afshar-Oromieh, A., Debus, N., Uhrig, M., Hope, T. A., Evans, M. J., Holland-Letz, T., Giesel, F. L., Kopka, K., Hadaschik, B., Kratochwil, C., & Haberkorn, U. (2018). Impact of long-term androgen deprivation therapy on PSMA ligand PET/CT in patients with castration-sensitive prostate cancer. European Journal of Nuclear Medicine and Molecular Imaging, 45(12), 2045-2054. doi: 10.1007/s00259-018-4079-z