Recent findings provide clues to the optimal timing and indications for the use of 68Ga-PSMA PET/CT in men with biochemically recurrent (BCR) prostate cancer after radical prostatectomy (RP), according to a presentation at the 37th congress of the European Association of Urology held in Amsterdam, The Netherlands.
In a study of 207 patients with a median age of 62 years who underwent 68Ga-PSMA PET/CT, investigators found that PSA levels and time to BCR at the time of PSMA PET/CT affect the probability of positive findings at PSMA PET.
Among men with early recurrence or PSA persistence after RP, the study showed that PSMA PET should be recommended even at low PSA levels given its high diagnostic value, according to investigators. The opposite may be true for patients with late BCR, who may not benefit from the addition of a PET PSMA scan. These patients should be counseled carefully based on PSA levels.
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“These results may help in sparing unnecessary exposure to radiation and prioritizing patients, as tracer production is time-consuming, especially for the 68 gallium PSMA,” said study investigator Daniele Robesti, MD, of IRCCS Ospedale San Raffaele, Division of Oncology Unit of Urology URI, Milan, Italy.
Selecting the most suitable candidates for 68Ga-PSMA PET/CT is critically important to spare low-risk patients from unnecessary staging procedures, according to Dr Robesti and colleagues. Until now, it has been unclear when to perform PSMA PET/CT based on PSA levels and time to BCR.
The researchers stratified patients according to time to BCR (12 months or less [early BCR] or PSA persistence vs more than 12 months [late BCR]) and analyzed the association between the PSA level at PSMA PET/CT and the probability of positive findings. The median PSA value at PSMA PET/CT was 1.0 ng/mL. Overall, 80 men (38%) experienced early BCR or PSA persistence after RP.
On multivariable analysis, higher PSA and early vs late BCR at PSMA PET were significantly associated with approximately 2.2- and 2.6-fold increased odds of positive results, respectively.
Among patients with early BCR, the probability of positive PSMA PET results was high even at low PSA levels and progressively increased with higher PSA level, the investigators reported. The rates of positive findings ranged from 63% to 93%. Conversely, in patients with late BCR, the probability of positive findings was lower than 40% for PSA values less than 0.5 ng/mL.
Given its high sensitivity compared with conventional imaging, PSMA PET may provide advantages to patients with oligometastatic cancer, where disease burden is low enough to be controlled with metastasis-directed therapy, thus delaying use of systemic agents, said Dr Robesti, who presented study findings.
José Ramón García Garzón, MD, of Medico CETIR Grupo Biomà dico ASCIRES, Barcelona, Spain, said it is important to know which patients may benefit the most. Therefore, screening in relation to the time after PSA elevation and the PSA value is an appealing strategy to increase the sensitivity of the test. “I am not surprised that PSMA positivity correlates with PSA elevation. However, the key question is whether detection of recurrence by PSMA allows differential treatment to be offered,” Dr Garcia said.
Douglas M. Dahl, MD, Chief of the Division of Urologic Oncology at Massachusetts General Hospital and Associate Professor of Surgery at Harvard Medical School in Boston, Massachusetts, said PSMA PET dramatically improves the ability to determine the location of prostate cancer recurrence or persistence after surgery or other treatments for localized prostate cancer. “As it has only recently become widely available in the US, we need to understand the best use and its limitations,” Dr Dahl said. “This study is important in that it finds that the test has different value in early versus late relapses.”
Otis W. Brawley, MD, a professor of oncology and epidemiology at Johns Hopkins University in Baltimore, Maryland, said there is excessive use of PET for patients with prostate cancer and other diseases. “Some patients are insisting on them for routine evaluation of response. That is clearly inappropriate use,” Dr Brawley said. “Some want them with very low PSA’s where chances of a false negative are high. When doctors do not have guidelines as to when a test should be used and there is a lot of patient request, things are ripe for waste and abuse.”
He said he has patients requesting this expensive test because they want “to see” their disease. What is greatly needed is a test that can determine if initial relapse is due to 1-3 sites of metastases, he said.
Reference
Robesti D, Mazzone E, Gandaglia G, et al. Optimizing timing and indications for 68Ga-PSMA PET/CT in patients with biochemical recurrent prostate cancer after radical prostatectomy. Presented at: EAU 2022, July 1-4, 2022, Amsterdam, The Netherlands. Abstract: A0190.
