“Biochemical recurrence” is the medical term for an increase in PSA after a man has had treatment for localized prostate cancer. The definition of biochemical recurrence may be different based on whether a man has had surgery (radical prostatectomy) or radiotherapy.

Until recently, computed tomography scans (CT), bone scans, and magnetic resonance imaging (MRI) were used to check for prostate cancer in these cases. But these types of images are rarely able to pinpoint the location of the prostate cancer, especially when the PSA is low.

A positron-emission tomography (PET) scan is a newer, more accurate way for doctors to check if and where prostate cancer has spread in your body. There are two FDA-approved PET CT scans that are often used in men with prostate cancer: fluciclovine F-18 PET CT (also called an Axumin PET CT scan) and prostate-specific membrane antigen (PSMA) PET CT.

Compared to Axumin PET CT, PSMA PET CT is better at finding prostate cancer in patients with biochemical recurrence. Because of this, most doctors will use this type of imaging to find cancer in the body, especially when the PSA is low (typically less than 2.0 ng/mL).

What is a PSMA scan?

PSMA is a protein found in the walls of prostate cancer cells. A PSMA scan combines an ingredient that targets the PSMA protein and a radioactive material (called a radiotracer) that can be seen with a PET scan. The imaging tracer only goes where there are cells with PSMA — mostly prostate cancer cells.

There are two common PSMA PET CT scans used in the United States. One is called the gallium (Ga) 68 PSMA-11 PET CT. This option is mostly only available in California. The second option is piflufolastat fluorine (F) 18-PSMA PET CT, also called a Pylarify PSMA PET CT scan. The Pylarify PSMA PET CT scan is more widely available across the country.

Both 68-Ga PSMA PET CT and Pylarify PSMA PET CT are FDA-approved for men who have developed a rising PSA after previous radiation or surgery.

What’s the evidence for PSMA scans in biochemical recurrence?

The CONDOR trial was the key trial that led to FDA approval for Pylarify PSMA PET CT in men with biochemically recurrent prostate cancer. This trial included 208 men with biochemical recurrence who had prior conventional imaging (CT, MRI, bone scan) that did not show visible prostate cancer. The purpose of the trial was to test how well Pylarify PSMA PET CT could correctly identify the location of prostate cancer in the body (compared to a biopsy or other type of imaging).

Among the men in this trial, 49.5% had already had a radical prostatectomy, 14.9% had had radiotherapy, and 35.6% had a radical prostatectomy followed by radiotherapy. Most men (66.8%) had a PSA between 0 and 2.0 ng/mL at the time of the study. Overall, 69.3% of men in the CONDOR trial had a PSMA-positive spot that could be seen on a PET CT scan.

Using these scans changed the treatment that men received. Overall, 64% of men in the CONDOR trial had a change in their treatment based on the results of the Pylarify PSMA PET CT. This included 79% of the changes after a positive scan (PSMA spot detected) and 21% of the changes after a negative scan (no PSMA spot detected). Future long-term studies are needed to assess the impact of these changes in treatment management. However, based on the results of this study, nearly two-thirds of men were appropriately treated after their Pylarify PSMA PET CT scan.

Keep in mind that just because the Pylarify PSMA PET CT shows a spot that is concerning for prostate cancer, it does not mean you have prostate cancer at that location. Similarly, just because the Pylarify PSMA PET CT does not show any spots concerning for prostate cancer, it does not mean you do not have prostate cancer in your body. More testing is needed to make sure if and where there is cancer.

PSMA PET CT is the most accurate imaging used to check for prostate cancer in the body when a patient has a biochemical recurrence. It can show if and where the prostate cancer has spread and allow for better treatment selection. If you have had previous treatment for localized prostate cancer and your PSA blood test shows possible biochemical recurrence, you should discuss whether a PSMA PET CT scan is right for you with your doctor.

Zachary Klaassen, MD, MSc
Urologic Oncologist, Georgia Cancer Center, Augusta University, Augusta, GA, USA