PSMA: New Gold Standard in Detecting Recurrent Prostate Cancer?
Not long ago I wrote an article on Axumin, a radioactive injection used in conjunction with a PET scan, to greatly improve the detection and location of recurrent prostate cancer. I won’t go into great detail here on how it works (you can check out the article link for that), but the short answer is that the Axumin links to amino acids that the cancer feeds on and then glows in the scan.
Axumin, however, is not the only PET scan being developed for prostate cancer. If anyone needs an example that prostate cancer research is moving forward it can be found in the fact that Axumin may be displaced as the primary method for finding recurrent PCa. In particular, the 68Ga-PSMA-11 PET/CT imaging scan (PSMA), “targets a specific molecule that is commonly present on the surface of prostate cancer cells.”1
How does a PSMA PET scan work?
What differentiates PSMA from other PET scans is that it is an actual enzyme located in prostate cancer cells and metastasis. The Axumin test, while a great leap forward, still relies on the cancer cells absorbing an outside substance faster than non-cancerous cells. Because prostate cancer generally grows slowly (even fast-growing PCa is often slower than many other cancers) it can be difficult for the PET to pick up, particularly at low PSA levels. Because the PSMA is a protein present on the PCa cancer cells, the test is not reliant on the rate of growth. Very small areas of cancer can be spotted at very low PSA.2
Evidence supporting the benefits of PSMA scans
Numerous studies have now looked at the superiority of PSMA compared to other PET scans (including Axumin), particularly when it comes to detecting PCa at low PSA levels. A 2016 paper in Cancer Imaging, which looked at multiple studies, noted that “Ga-PSMA ligand PET imaging has been shown to increase detection of metastatic sites even at low PSA-values in comparison to conventional imaging or PET examination with different tracers.”3
A study published in the Journal Lancet Oncology of a clinical trial details what is claimed to be the first prospective head to head examination of PSMA vs. Axumin. They state “The aim of this study was to compare prospectively paired 18F-fluciclovine and PSMA PET-CT scans for localizing biochemical recurrence of prostate cancer after radical prostatectomy in patients with low prostate-specific antigen (PSA) concentrations (≤2·0 ng/mL).” The study consisted of 50 patients with PSA between 0.2 and 2.0 ng/ml. They underwent Axumin and PSMA PET scans within 15 days. Detection rates were significantly lower for Axumin – 26 to 56%. The authors conclude that “With higher detection rates, PSMA should be the PET tracer of choice when PET-CT imaging is considered for subsequent treatment management decisions in patients with prostate cancer and biochemical recurrence after radical prostatectomy and low PSA concentrations (≤2·0 ng/mL).”4
The future of prostate cancer screening research
There are currently multiple additional ongoing clinical trials. PSMA PET scans have not yet been approved by the FDA, but there are multiple locations it is available in the U.S. due to research activity. Hopefully, it will soon be available at a lot more.
One final note: there is another potential therapeutic advantage of PSMA above and beyond other PET scans. There is the possibility of linking more powerful radioactive substances to PSMA ligands, which may be able to actually kill cancer cells.5 With any luck, this potential will progress enough for an article for another day.
Have you made personal connections through your journey with prostate cancer?