New Imaging Test Locates Prostate Cancer Cells Hiding in the Body
The FDA approved a new, more precise method of finding even the tiniest amounts of metastatic prostate cancer spread throughout in the body. The test, called a PSMA-PET scan, will make it easier to diagnose—and treat—metastatic prostate cancer sooner.
The test uses a tracer drug called Gallium 68 PSMA-11. When injected, the drug travels throughout the patient’s body and attaches to proteins called PSMA, which appear in high levels in prostate cancer cells. The drug is radioactive, so the cancer cells that the drug is attached to appear as bright spots the PET scan image. Thus, doctors can clearly see where—and how much—the cancer has spread throughout the body.
The PSMA PET scan gives a brighter, more precise picture than other types of scans and can reveal very small cancer cell clusters. Without this test, these cancer cells might have remained hidden until the disease spread further and caused symptoms, also becoming much more difficult to treat.
This advancement in locating prostate cancer cells anywhere in the body gives patients and doctors important information to make personalized treatment decisions.
Who should get the new PSMA imaging test?
The FDA has approved the test for two kinds of patients, for which researchers evaluated safety and efficacy in clinical trials.
The first group is patients who are newly diagnosed with prostate cancer after having a biopsy. Certain factors may lead the patient’s doctor to suspect that the cancer has spread outside the prostate, such as a very high PSA or a high Gleason grade from the biopsy. Before proceeding with surgery to remove the prostate, the patient could have a PSMA PET scan. If this revealed cancer spread beyond the prostate, the surgery would not remove or cure all the cancer. Instead, radiation, hormonal therapy, or new immunotherapy treatments would be better first-line approaches to target the disease and its spread.
The second group is patients with rising PSA levels after their initial prostate cancer treatment, either prostate surgery or radiation. A post-treatment increase in PSA levels indicates that the cancer has come back, also called cancer recurrence. The PET scan can confirm this finding, and thus the patient and his doctor can decide how to next proceed on targeting the cancer.
The future of the PSMA drug could help patients
Researchers at the University of California, where Gallium 68 PSMA-11 was tested, are now hoping that the same drug could be used to target and destroy cancer cells, not just find them. They are currently experimenting to see if attaching a cancer-fighting drug to the Gallium 68 PSMA-11 will deliver the medicine directly to the cancer cells.
At this time, the PSMA PET test is only available at the University of California sites in Los Angeles and San Francisco. However, other PSMA- targeting drugs are being developed elsewhere.
Northwestern Medicine has a PSMA scanner, but at present, it can only be used for patients enrolled in a specific research protocol. However, it will soon become available for use in clinical practice.
Two other PET drugs are approved for use only in patients with suspected cancer recurrence, but they do not target the PSMA protein in the same way.
What is a PET scan?
PET=positron emission tomography. A PET scan is an imaging test that uses a radioactive “tracer drug,” sometimes called a dye, that the PET scanner detects wherever it is in the body. Different types of “tracers” will move to different parts of the body, depending on the purpose of the PET scan. The “tracer” shows up as a bright spot on the PET scan image.