A recently published blog post discussed a newly approved imaging agent with an awkward name: Gallium-68 PMA-11. This minimally radioactive tracer is released in small amounts by injection and adheres to prostate cancer cells, which then glow and show up on positron emission tomography (PET). This type of imaging, offered to men with rising PSA levels after their first treatment for prostate cancer (a condition called biochemical relapse), allows doctors to find and treat new tumors that they might otherwise miss. With the imaging technology currently available, such tumors could potentially escape detection until they are larger and more dangerous.
Gallium-68 PMA-11 may be the latest PET tracer to receive FDA approval, but not everyone can get it. In the US, it is currently only available to patients treated at the University of California at Los Angeles or the University of California at San Francisco, where the tracer is made. However, two other PET tracers approved in the US for imaging prostate cancer are becoming more accessible.
In January 2021, a Stanford University team released results showing that one of these tracers, Fluciclovine F18 (trade name Axumin), identified significantly more metastatic cancers than other conventional types of imaging. Axumin was approved in 2016. This is the first data to show how well the tracer works in real-world environments.
Stanford researchers reviewed the medical records of 165 men who received Axumin PET scans between September 2017 and December 2019. All men had a biochemical recurrence, and 70 of them were also imaged using other technologies, including CT scans, bone scans, or MRIs.
Axumin PET scans outperformed all other tests for tumor detection. A total of 110 men had PET-detected metastases, and none with a negative PET scan were positive for cancer on other imaging tests. PET imaging found cancer in nine of 31 men who had negative results on CT scans. Similarly, six out of 31 men with negative MRI results had PET-detected tumors. The technology also found skeletal tumors in a man with a negative bone scan.
It is important that the tumor detection rates were highest in men with high and rapidly rising PSA levels. This is to be expected as prostate cancer cells release PSA. As tumors grow and multiply, PSA levels rise at the same time. In fact, previous research shows that axumin PET scans are unlikely to detect cancer if the PSA level is less than 1 nanogram per deciliter (ng / ml) in the blood.
Positive PET scans also resulted in treatments that doctors might not have started if only negative results were available with other imaging tests. Most of the 102 men who were subsequently treated received radiation that was specifically delivered to the tumor sites, in some cases combined with drugs that block testosterone, a hormone that accelerates the growth of prostate cancer.
The study had several limitations, including the fact that it was only conducted in one facility. In addition, in only seven cases, PET findings were confirmed by a pathologist reviewing the tissue samples taken. This is because, in most cases, the lesions detected were too small – less than an inch – to do a biopsy. PET-detected cancers were instead confirmed by a decrease in PSA after treatment.
“Axumin scanning and newly developed gallium scanning are changing the way prostate cancer is staged and ultimately treated,” says Dr. Marc Garnick, Professor of Medicine at Gorman Brothers at Harvard Medical School and Editor of the Beth Israel Deaconess Medical Center of Harvard Health Publishing Annual report on prostate diseasesand Editor-in-Chief of HarvardProstateKnowledge.org. “The increased sensitivity of these new scanning technologies both identifies patients with metastatic disease who would otherwise have been classified as metastasis-free, as well as confirming the absence of metastatic deposits. Both situations will change the way treatment decisions are made, and this will provide more precision in what we can offer our patients. These new technologies are good news for doctors and patients. “