Molecular Imaging PSMA PET/CT Could Transform Management of People with Aggressive Cancer

Upon recent discussions with my urologist and oncologist, they both informed me that the following is a highly significant development in imaging of prostate cancer.

A medical imaging technique, known as PSMA PET/CT, that provides detailed body scans while detecting levels of a molecule associated with prostate cancer could help doctors better tailor treatments for their patients, by determining the extent of disease spread at the time of diagnosis. This was the finding of a randomized, controlled trial involving 300 patients in Australia recently published in The Lancet journal.

The approach combines two imaging technologies – positron emission tomography (PET) and computed tomography (CT) – and is almost one third more accurate than standard CT and bone scans at pinpointing the spread of prostate cancer throughout the body. PSMA PET/CT proved to be 92% accurate compared with only 65% accuracy with standard imaging. Although the study did not assess whether the scans had any effect on patient survival, the researchers say this approach could improve outcomes by helping doctors decide whether to offer a localized treatment, such as surgery or radiotherapy, or to use more advanced treatments to treat the whole body if the cancer has already spread.

Prostate cancer is commonly treated by surgery to remove the prostate or intensive radiotherapy to target the tumor. If there is a high risk the cancer may have spread to other parts of the body, patients may be offered medical imaging – typically CT and bone scans – to help doctors determine if additional treatments are needed. Study lead Professor Michael Hofman of the Peter MacCallum Cancer Centre, Melbourne, said: “Taken together, our findings indicate that PSMA-PET/CT scans offer greater accuracy than conventional imaging and can better inform treatment decisions. We recommend that clinical guidelines should be updated to include PSMA PET/CT as part of the diagnostic pathway for men with high risk prostate cancer.” Both imaging techniques involve exposure to radiation but the dose associated with PSMA-PET/CT was less than half that associated with conventional imaging (8.4mSv vs 19.2mSv).

Researchers sought to investigate if a molecular imaging approach could help doctors better define the extent of disease at the time of diagnosis. This approach involves giving patients a radioactive substance that detects a molecule called Prostate Specific Membrane Antigen (PSMA), which is found at high levels on prostate cancer cells. They 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.

The study involved 300 men recruited to ten sites across Australia. All of the men had been diagnosed with prostate cancer, confirmed by tests on prostate tissue samples, and were deemed to be at high risk of having aggressive disease. The men were randomly assigned to receive either conventional CT and bone scans (152 patients) or PSMA-PET/CT (148 patients). Men then swapped over and were given the scans using the alternative imaging arm unless more than three sites of cancer spread were detected on the initial scans (18 patients). A second round of scans were undertaken at six months if there was any concern about ongoing prostate cancer following treatment. The results of these scans were used to confirm tumor spread, in addition to biopsies and change in blood tests.

Overall, the researchers found the PSMA-PET/CT scans were much more accurate than conventional CT and bone scans at detecting cancer spread (92% vs 65%). This is because the new technique was better at detecting small sites of tumor spread. Conventional imaging failed to detect that the cancer had spread in 29 patients, giving a false negative result. By comparison, PSMA-PET/CT gave false negative results in just six patients. Furthermore, fewer men had false positive results obtained with the new technique (2 with PSMA-PET/CT and 9 with conventional imaging)

PSMA-PET/CT scans had greater impact on the way patients’ disease was managed, with 28% having their treatment plans changed after the scans (41/147) compared with 15% following conventional imaging (23/152). When PSMA-PET/CT was given at the second round of imaging after conventional imaging, disease management plans were still changed in more than a quarter of cases (39/146, 27%). When conventional imaging was used at the second round, however, just 5% of patients had their treatment plans changed (7/135 patients).

Professor Declan Murphy, senior author, of Peter MacCallum Cancer Centre, Melbourne, said “Around one in three prostate cancer patients will experience a disease relapse after surgery or radiotherapy. 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.”

For further details, see the following from the Prostate Cancer Foundation, March 22, 2020.