New imaging technology less accurate than MRI

A team of researchers in Australia and New Zealand found that MRI scans can detect prostate cancer more accurately than the newer, prostate-specific PSMA PET/CT scanning technique.

The findings are being presented today at the European Association of Urology (EAU22) Annual Congress in Amsterdam.

Prostate-specific membrane antigen (PSMA) PET/CT scans, approved by the US FDA in 2020, use a radioactive dye to “light up” areas of PSMA, which is found on the surface of prostate cancer cells. They are currently used to treat prostate cancer because they can accurately measure the progression or recurrence of the disease. So, in this trial, researchers set out to find out if they could also be used to diagnose prostate cancer.

The PEDAL trial enrolled 240 patients in five hospital groups who were at risk of prostate cancer. An MRI scan and a PSMA PET/CT scan were performed on each patient. If imaging suggests the presence of prostate cancer, a biopsy is performed by the patient’s urologist.

MRI scans detected abnormalities in 141 patients, while PSMA PET/CT scans detected abnormalities in 198 patients. A total of 181 patients (75%) underwent prostate biopsy, and 82 of these patients were subsequently found to have clinically significant prostate cancer.

Because each patient had both types of scans, the researchers could assess which type more accurately detected those patients who had prostate cancer. The researchers found that MRI scans were significantly more accurate at detecting any grade of prostate cancer than PSMA PET scans (0.75% for MRI versus 0.62% for PSMA PET).

Associate Professor Lih-Ming Wong, consultant uro-oncologist at St Vincent’s Hospital in Melbourne, Australia, led the research team. He said: “Our analysis found that MRI scans were better than PSMA-PET for detecting any grade of prostate cancer. When we looked only at clinically significant prostate cancers, there was no difference in accuracy. As this study is one of the first to investigate the use of PSMA-PET to diagnose prostate cancer, we are still learning and fine-tuning how to improve the use of PSMA-PET in this setting.

Although detection thresholds will be fine-tuned as diagnostic use develops, Professor Wong believes the trial has important lessons for clinicians.

He says: “This study confirms that the existing ‘gold standard’ for pre-biopsy detection – MRI – is indeed a high standard. Even with fine-tuning, we suspect that PSMA PET/CT will not replace MRI as the primary modality for prostate cancer detection. But it is likely to have future use as an adjunct to MRI, either for people for whom MRI is unsuitable, or as a single combined ‘diagnosis and staging’ scan in appropriately selected patients.”

He continues, “That’s why these types of robust studies are critical so that we can better understand the role these technologies can play at each stage of the cancer journey and advance the management of prostate cancer.”

Professor Peter Albers, Chair of the Chief Scientific Office of the European Association of Urology, commented: “New diagnostic tools need to be tested as carefully as new drugs, so we welcome the findings of this landmark Phase III trial, which showed that MRI is better at detecting prostate cancer.

“It also showed that PSMA PET/CT was non-inferior to MRI in detecting clinically significant cancers (ISUP 2 and higher); and since the ultimate goal of primary staging will be to detect only the more aggressive cancers and avoid unnecessary biopsy, this is not the end of the story. More research will be needed to investigate the PSMA PET/CT correlation between standard uptake value (SUV) and cancer aggressiveness, but the first steps towards finding the best diagnostic approach to clinically significant prostate cancer have been made .

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