A recent blog post discussed a newly approved imaging agent with an unwieldy name: gallium-68 PMA-11. Delivered in small amounts by injection, this low-radioactive tracer adheres to prostate cancer cells, which then glow and show up on a positron emission tomography (PET) scan. Offered to men whose PSA levels rise after the initial treatment for prostate cancer (a condition called biochemical recurrence), this type of imaging can help doctors find and treat new tumors that they might otherwise miss. With the imaging technology currently available, these tumors could potentially escape detection until they are larger and more dangerous.
But while gallium-68 PMA-11 is the latest PET tracer to get FDA approval, not everyone can get it. In the United States, it is currently only available to patients treated at the University of California, Los Angeles or the University of California, San Francisco, where the tracer is manufactured. However, two other PET tracers approved for imaging prostate cancer in the United States are increasingly available.
In January 2021, a team from Stanford University published results showing that one of these tracers, called fluciclovine F18 (trade name Axumin), identified significantly more metastatic cancers than other conventional types of imaging. Axumin was approved in 2016, and this is among the first data to show the performance of the plotter in real environments.
Stanford researchers looked at the medical records of 165 men who had received Axumin CT scans between September 2017 and December 2019. All of the men had a biochemical recurrence, and 70 of them were also imaged with other technologies, including CT scans, bone scans, or MRIs. .
Axumin PET scans have outperformed all other tests when it comes to tumor detection. In all, 110 men had metastases detected by PET, and no one with a negative PET was positive for cancer on other imaging tests. PET imaging revealed cancer in nine of 31 men who tested negative on a CT scan. Likewise, six of 31 men with negative MRI results had tumors detected by PET. The technology has also detected skeletal tumors in a man with a negative bone scan.
Importantly, tumor detection rates were highest in men with high and rapidly increasing PSA levels. This is normal, since prostate cancer cells release PSA; As tumors grow and proliferate, PSA levels will rise in tandem. In fact, previous research shows that Axumin PET scans are unlikely to detect cancer if the PSA is less than 1 nanogram per deciliter (ng / mL) in the blood.
Positive PET scans have also led to treatments that doctors may not have started if only negative results with other imaging tests were available. Most of the 102 men who were subsequently treated received rays delivered specifically 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 some limitations, including the fact that it was conducted at only one facility. In addition, in only seven cases, the PET results were confirmed by examination by a pathologist of the tissue samples taken. This is because in most cases the lesions detected were too small – less than an inch in size – for a biopsy. Rather, cancers detected by PET were confirmed by drops in PSA after treatment.
“Axumin scanning, along with the newly developed gallium scan, is changing the way prostate cancer is staged and ultimately treated,” says Dr Marc Garnick, Gorman Brothers professor of medicine at Harvard Medical School and Beth Israel Deaconess Medical Center, Editor-in-Chief. from Harvard Health Publishing Annual report on prostate diseases, and editor of HarvardProstateKnowledge.org. “The increased sensitivity of these new scanning technologies allows both to identify patients with metastatic disease who would otherwise have been considered free from metastases, as well as to help confirm the absence of metastatic deposits. Both situations will change the way treatment decisions are made, and this will provide more precision in terms of what we can offer our patients. These new technologies are good news for doctors and patients. “