Prostate cancer recurs up to 40% of the time within ten years after initial treatment. But until recently, there has not been a test that could detect a recurrence before the cancer is already at an advanced stage…and harder to treat. Good news: A new kind of scan finds prostate cancer recurrence months or even years before other tests can. If you (or someone you know) has been treated for prostate cancer, here’s what you need to know—it could save your life.
Rising levels of prostate specific antigen (PSA) is the classic sign that prostate cancer has recurred. Doctors then order tests to see whether the recurrence is local (in the prostate) or has spread (metastasized). PSA is a protein produced by prostate cells that can indicate a relapse after treatment. (Treatment lowers PSA to nearly zero or zero, depending on the treatment.) The higher the PSA level, the more prostate cancer cells there are producing the protein. Up until now, the tests available—such as a bone scan or positron emission tomography (PET) scan—have been able to detect recurrence only when the growing cancer has caused PSA levels to rise to at least 10 nanograms per milliliter (ng/mL) to 30 ng/mL or even higher. At that point, the cancer has advanced, is much harder to treat…and outcomes are poorer.
The good news is that there is now a new kind of PET scan that can detect recurrence at much earlier stages than any other test currently available—with tremendous lifesaving potential. But first, some background on PET scans.
How a PET Scan Works
All PET scans involve injection of a radioactive tracer, followed by a computed tomography (CT) scan of the patient’s whole body. Depending on the type of PET, radioactive tracers include a radioactive drug that gravitates to damaged cells in bones…a sugar (fluorodeoxyglucose /FDG) that is absorbed by glucose molecules in cells…a radioactive form of the vitamin-like nutrient choline, called Choline C 11 that is also absorbed by cells, similarly to FDG.
The different tracers all work on the same principle—that cancer cells multiply more rapidly than normal cells and don’t undergo normal cell death, so more of the tracer ends up in the cancer cells, which makes those cells “light up” on a scan. However, there are also differences…
• A bone scan is able to detect cancer in bones when PSA is as low as 10 ng/mL but is not able to detect cancer metastasis in other parts of the body, such as the prostate or lymph nodes.
• An FDG PET can detect cancer recurrence in other parts of the body, but only once the cancer has spread away from the area of the prostate. The FDG PET is not able to detect the difference between cancer and benign prostatic hypertrophy—the main reason this scan is falling out of use.
• Choline C 11 PET is more sensitive than FDG or a bone scan—it detects cancer when PSA is as low as 2 ng/mL. But the radioactive choline has a very short shelf life. It can be made only in specialized facilities (Mayo Clinic is one of them) and must be given to patients within minutes of being produced. So the scan is not widely available.
Note: There is also a kind of PET scan that uses a tracer that binds to an enzyme in prostate cancer cells, prostate-specific membrane antigen/PSMA. PSMA PET can detect cancer when PSA levels are as low as 1 or 2 ng/mL. But while popular in Europe, the scan is approved in the US only for research.
A New and Better PET
Recently, the FDA approved a new type of PET scan called Axumin. Axumin PET uses an amino acid antibody that binds to PSA proteins in blood. Not only do prostate cancer cells “eat up” this amino acid more quickly than is the case with other tracers—so the patient doesn’t have to spend a long time waiting for the tracer to circulate through his body—but the cancer cells that the tracer attaches to are at a very early stage of cancer development. Axumin PET can detect prostate cancer when PSA produced by the cancer cells is as low as 1 ng/mL. No bone, MRI, or CT scan can find prostate cancer any earlier.
Studies show that Axumin PET scan has a success rate for finding early recurrence comparable to the PSMA and better than Choline C 11—but with the big advantage that it’s more available. Axumin PET is available at many US prostate cancer “centers of excellence” treatment centers and is also covered by Medicare.
Bottom Line
If you have been treated for prostate cancer, your PSA should be undetectable after surgery or very low after radiation treatment. If your PSA starts to go up, especially if the level is rising rapidly, ask your doctor about Axumin PET—it could be a lifesaver.
