Molecule May Predict Prostate Cancer's Return
WEDNESDAY Aug. 15, 2007 -- For the first time, scientists say they have identified an immune molecule that may predict prostate cancer recurrence after surgery.
"We discovered a protein that shows up in prostate cancer cells, and this protein is thought to be involved in shutting down immune responses in the body," said lead researcher Dr. Eugene D. Kwon of the Mayo Clinic, in Rochester, Minn.
The molecule, called B7-H3, is found on the surface of prostate cancer cells, and it kills or paralyzes immune cells that are attacking cancer cells, Kwon explained.
"The most aggressive tumor cells have the highest levels of this protein," he said. "The other surprising finding was that when we examined 338 men who had had radical prostatectomy and then followed those patients, we found that the patients who had the highest levels of this protein were at highest risk of having recurrence of their prostate cancer."
The report appears in the Aug. 15 issue of Cancer Research.
The researchers found that all tumors and precancerous tissues had B7-H3, but patients with the highest levels were four times more likely to experience cancer recurrence compared to those with lower levels of B7-H3 within their tumors. Those with moderate levels of B7-H3 had a 35 percent higher risk of recurrence.
Kwon said that B7-H3 acts as a "crystal ball" to tell whether or not the tumor can come back after surgery.
The researchers also believe that by testing the levels of B7-H3, they might be able to determine which patients are good candidates for surgery.
"Patients at high risk for failing surgery may not be good candidates for surgery alone," Kwon said. "In addition, we may be able to sort out, for patients who don't want any treatment, whose cancers are more likely to benefit from 'watchful waiting.'"
In addition, B7-H3 could become a target for therapy, Kwon said. "We could block this molecule and make the cancer more responsive to the body's immune response," he explained.
One expert isn't so sure the finding is a great advance.
"What needs to be done is [for the researchers] to show us what this marker tells us that we don't already know from other markers," said Dr. Anthony D'Amico, chief of radiation oncology at Brigham and Women's Hospital in Boston. "We can't tell from this study whether this marker is providing new information or information that's already contained in other markers."
If the marker does add something new it would be important, D'Amico said. "Any marker that provides us with additional information about prognosis sets itself up as a target for future therapies," he noted.
Another expert suspects B7-H3 might prove very useful in the future.
"The problem in prostate cancer is that we know we diagnose a lot of prostate cancer, but we know that only a small number of them will go on to really cause a man difficulty," said Dr. Len Lichtenfeld, deputy chief medical officer for the American Cancer Society.
The goal is to find markers that sort prostate cancers into aggressive and less aggressive types, Lichtenfeld said. "This marker may help us in this process," he added.
He also believes more biomarkers are yet to be identified.
"Ultimately, when someone is diagnosed with prostate cancer we will take a look at their cancer tissue and look at many of these markers and be able to come up with a profile that gives us much more accurate information about prognosis and treatment," Lichtenfeld said.
For more information on prostate cancer, visit the American Cancer Society.
Posted: August 2007
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