For men diagnosed with prostate cancer, a clinical trial indicates that PSMA PET-CT imaging is more effective in detecting the spread of cancer to other body parts compared to the standard approach using CT and bone scans. The Australian trial, published in The Lancet, demonstrated that PSMA PET-CT was substantially more likely to detect metastatic tumors in men diagnosed with localized prostate cancer at high risk of spreading beyond the prostate.
Superior Accuracy of PSMA PET-CT
The trial, led by Michael Hofman from the Peter MacCallum Cancer Centre, found PSMA PET-CT to be 27% more accurate than the standard approach in detecting metastases (92% versus 65%). Accuracy was determined by combining the scans’ sensitivity and specificity. PSMA PET-CT was also more accurate for metastases in lymph nodes and distant parts of the body, including bone. Radiation exposure was substantially lower with PSMA PET-CT compared to conventional methods.
Impact on Treatment Strategies
The imaging results significantly influenced clinicians’ treatment choices. Based on the findings, the initial treatment plan was altered for 28% of men who underwent PSMA PET-CT, compared to 15% of those who had conventional imaging. According to Dr. Hofman, detecting metastases early is key to optimizing treatment, as treating the primary tumor in the prostate is futile if the cancer has already spread.
FDA Approval and Availability
As of December 1, 2020, the FDA approved the radioactive tracer Gallium (Ga) 68 PSMA-11 for PET imaging in men with prostate cancer. This tracer can be used for prostate cancer suspected of spreading or recurring after successful treatment, indicated by elevated PSA levels. Prior to this approval, PSMA PET-CT was only available in the United States within clinical studies.
How PSMA PET-CT Works
PSMA PET-CT combines CT scans with PET scans, using a radioactive tracer injected intravenously. This tracer includes a molecule that binds specifically to the PSMA protein, which is abundant on prostate cancer cells. The radioisotope used in the Australian trial was gallium-68 (Ga-68). Martin Pomper, M.D., Ph.D., from Johns Hopkins School of Medicine, noted that smaller studies have suggested PSMA PET-CT is superior in detecting metastases, leading to anticipation for larger studies.
Advantages Over Conventional Imaging
Conventional CT and bone scans have limitations in detecting individual prostate cancer cells and can miss small tumors. Bone scans may also produce false positives due to non-cancerous bone abnormalities. PSMA PET-CT is more specific in identifying prostate cancer cells, reducing the likelihood of inconclusive results. The trial found that PSMA PET-CT was much less likely to produce equivocal results (7% versus 23%), minimizing the need for additional tests.
Future Directions
With the FDA approval of Ga 68 PSMA-11, PSMA PET-CT is expected to become more widely available in the United States. Researchers are also exploring the use of PSMA PET-CT for other cancers where PSMA is highly expressed, such as kidney, thyroid, and breast cancers. Jeremie Calais, M.D., of UCLA's Jonsson Comprehensive Cancer Center, mentioned that UCLA and UCSF have filed applications for Ga-68 PSMA-radiotracer approval, potentially allowing other institutions to produce their own tracers.
