An imaging technique known as PSMA PET/CT can detect disease spread at diagnosis more effectively than conventional scans, helping doctors to prescribe appropriate treatments.
A different kind of scan than usually used to image prostate cancer is more accurate at finding disease spread and should become part of routine clinical practice for men with high-risk localized prostate cancer, a study in The Lancet
The molecular imaging technique could help doctors to better select the most appropriate treatments for their patients by determining at diagnosis the extent of the prostate cancer’s spread, according to findings from the randomized, controlled trial. While local disease may be treated with surgery to remove the prostate or radiotherapy to shrink the tumor, systemic treatments that work throughout the body, such as chemotherapy or hormonal therapy, can be introduced if there’s evidence the cancer has spread.
Currently, doctors who suspect spread check with CT and bone scans.
"Around one in three prostate cancer patients will experience a disease relapse after surgery or radiotherapy,” Dr. Declan Murphy, the study’s senior author and director of genitourinary oncology and robotic surgery at the Peter MacCallum Cancer Centre in Melbourne, Australia, said in a press release. “This is partly because current medical imaging techniques often fail to detect when the cancer has spread, which means some men are not given the additional treatments they need. Our findings suggest PSMA-PET/CT could help identify these men sooner, so they get the most appropriate care."
The imaging technique the researchers tested is known as PSMA PET/CT. Patients undergoing the imaging are given a radioactive substance that detects the protein PSMA, which is found at high levels on prostate cancer cells. Patients then undergo a PET/CT scan. The CT scan produces detailed images of the body's organs and structures, while the PET scan lights up areas where PSMA is present at high levels, indicating the presence of prostate cancer cells, according to the release issued by The Lancet
The method is nearly one-third more accurate than standard imaging at detecting the spread of prostate cancer through the body, the researchers found. PSMA PET/CT demonstrated an accuracy of 92%, compared with 65% when using standard imaging, they reported.
Both imaging techniques involve exposure to radiation, but the dose associated with PSMA PET/CT was less than half of that associated with conventional imaging.
The study did not assess whether the scans had any effect on patient survival.
The study took place at 10 sites across Australia and included 300 men with prostate cancer who were considering surgery or radiotherapy with curative intent and had at least one high-risk factor, such as a prostate-specific antigen concentration of 20 ng/mL or higher or a clinical stage of T3 or worse. Between March 22, 2017 and Nov. 2, 2018, the men, whose median age was 68, were randomly assigned to receive either conventional CT and bone scans (152 patients) or PSMA PET/CT (148 patients).
Shortly after that imaging was completed, men in the conventional group received scans using PSMA PET/CT and men in the PSMA PET/CT group received conventional imaging to allow comparison between the two methods.
Finally, at a six-month follow-up appointment, participants received a second round of medical imaging to look for further disease spread. Men received imaging consistent with their assigned group, although those in the conventional group were allowed to receive PSMA PET/CT scans if doctors suspected they had remaining or recurrent cancer.
PSMA PET/CT scans were more accurate than conventional CT and bone scans because they were better at detecting small sites of tumor spread, the researchers concluded.
In initial imaging, PSMA PET/CT scans had a greater impact on treatment, with 28% (41 of 147) of men having their treatment plans changed after the molecular scans compared with 15% (23 of 152) following conventional imaging. After the men switched scanning methods for their second round of imaging, 5% (seven of 136) had their treatment plans changed after conventional imaging versus 27% (39 of 146) after PSMA PET-CT.
The researchers found that conventional imaging failed to detect cancer’s spread in 29 patients, giving a false negative result. By comparison, PSMA PET/CT gave false negative results in six patients. Furthermore, false positive results were more frequent with conventional imaging (nine patients) than with PSMA PET/CT (two patients).
Seven percent of patients who underwent PSMA PET/CT scans had ambiguous results, versus 23% of patients who had conventional imaging.
Paying for Molecular Imaging
Whether this new method of imaging is feasible for widespread use will depend, in part, on its costs.
Study co-author Dr. Roslyn Francis, an associate professor at the University of Western Australia, noted in the press release that "costs associated with PSMA-PET/CT vary in different regions of the world, but this approach may offer savings over conventional imaging techniques. A full health-economic analysis will help to determine the cost effectiveness of introducing PSMA-PET/CT, both from a patient and a healthcare perspective."
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