A new diagnostic scan could help localize recurrent cancer in men who have had surgical removal of their prostates but still show indications of metastasized cancer.
"The first sign of recurrence will be elevated levels of [a marker] which tells the physician that a cancer is present but doesn't tell them where. You want to have an imaging test that tells you where because [the scan] will affect how you treat it," said the report's senior author Dr. Thomas Polascik, assistant professor in the division of urology. "In the past, without this diagnostic scan, you could give a therapy that might not be in [the] best interest of the patient. If used properly, this scan gives a physical tool to determine exactly where the tumor is and how to treat it properly."
The study, published in this month's issue of the journal Cancer, examined 265 prostate cancer patients who had undergone radical prostatectomies, or prostate removal, from 75 sites from across the country. The scan, called a capromab pendetide scan, identified recurrent prostate cancer in 72 percent of the men.
Other imaging scans may not be as sensitive: Bone scans, which can only detect diseases in bones, showed 11 percent of the group had recurrent disease while computerized tomography scans, which are non-specific and can only image soft tissue greater than a certain diameter, identified 16 percent of the men as having recurrence. Furthermore, these two scans were less specific in identifying the site and extent of cancer recurrence.
When a patient has his prostate removed, the level of a substrate called prostate specific antigen should be zero. The first sign of recurrence is an elevated post-operative PSA level. Patients are given a radioactively labeled monoclonal antibody that targets and binds to PSA found on prostate membranes. This acts as a tracer, specifying the cancer's site.
"The real significance of this scan is its ability to image recurrent diseases. It's the first time it's been clearly determined that you can image a disease with really low PSA levels," Polascik said.
If a cancer is localized, physicians will typically suggest using radiation as treatment. Other therapies, though, such as hormone treatments, are more effective if the cancer is widespread, or distant.
"Using this technique will help minimize the number of people unnecessarily treated with radiation," said lead author Dr. Ganesh Raj, a senior resident in the division of urology. "It helps you target therapies more effectively and identifies the people who would benefit most from these treatments."
One limitation of the study, however, is that the researchers lack histological evidence, such as tissue samples from the suspected area, to confirm the scan's results. However, previous studies have shown that a positive scan correlates well to histologic evidence of metastatic prostate cancer.
Right now, the scientists are interested in developing other scanning techniques that could provide more information about recurrence.
"We're doing studies that will combine the technology of CT scans with that of [capromab pendetide] scans. By combining these two kinds of imaging studies, we could get information about where the disease is located and what it looks like in three dimensions," Polascik said.
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