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Goal of New Test Is to Determine Which Men Will and Will Not Need Treatment for Prostate Cancer
WebMD Health News
Reviewed By Laura J. Martin, MD
April 20, 2010 (Washington, D.C.) -- Researchers are developing a new blood test to help identify which men with early prostate cancer can forgo immediate treatment.
In a small preliminary study, the test proved 70% accurate in predicting which men had more aggressive tumors that require treatment.
The results have yet to be replicated, a necessary step before acceptance by the medical community.
But the test shows promise for safely identifying men who can undergo active surveillance -- close monitoring for signs of tumor growth -- rather than treatment, says Robert W. Veltri, PhD, an associate professor of urology and oncology at Johns Hopkins University.
"The goal of the new test, which measures blood levels of three different forms of PSA, is to determine who will and who will not progress and require treatment," Veltri says.
The findings were presented at the annual meeting of the American Association for Cancer Research.
Prostate Cancer: To Treat or Not?
Because prostate cancer often grows so slowly it may never become life-threatening, many of these men, particularly older men, may die of other causes before the prostate cancer causes problems. But in some men, the cancer will spread beyond the prostate without treatment. Then it may no longer be curable.
As a result, there has been a long-running debate in the medical community about the value of treatment to destroy cancer cells vs. active surveillance, also known as watchful waiting.
Watchful waiting consists of close monitoring with periodic digital rectal exams, yearly biopsies, and PSA (prostate-specific antigen) blood tests.
New Prostate Cancer Test Shows Promise
"Because of PSA, there is overdiagnosis and overtreatment of prostate cancer," he says.
The new blood test, known as the Prostate Health Index (PHI), measures three forms of PSA, including pro-PSA. Pro-PSA is a shortened molecule that is missing a few of the amino acids that make up the PSA protein. It's the most accurate form of PSA, Veltri says.
The federally funded study involved 71 men who were diagnosed as having small, low-grade, and low-stage prostate cancer based on their PSA results. At the time of their diagnosis, their blood had been banked.
By an average of nearly four years later, 39 had unfavorable biopsy results that signaled a need for treatment.
The PHI test was performed on blood samples from all 71 men.
"When we combined the [biopsy results] and the serum Prostate Health Index, we were able to predict seven in 10 men that might progress," Veltri says.
Veltri says the PHI test won't replace biopsies but will hopefully allow men to have them every other year instead of year.
His lab is now conducting an expanded study to look for other biomarkers that may predict aggressive cancers.
Test May Predict Prostate Cancer Spread
Also at the meeting, researchers reported using a microchip to detect circulating tumor cells in the blood of people with prostate cancer.
The presence of circulating tumor cells, or CTCs, in the blood is an indication of cancer spread, says Sunitha Nagrath, PhD, an instructor of surgery and bioengineering at Harvard Medical School.
CTCs also carry molecular signatures that can be used to guide targeted drug therapy, she says. The problem: There are only a few CTCs in millions of cells, she tells WebMD. "It's like looking for a needle in a haystack."
The CTC-chip can capture about 200 circulating tumor cells from a teaspoon of blood, she says.
In a small pilot study, the researchers found CTCs in nearly half of 20 people with early-stage prostate cancer and in two-thirds of people with advanced cancer.
"We think that's an indicator they are more prone to metastasis (cancer spread), but that remains to be proven," Nagrath says.
The test is not commercially available.
"Eventually we hope that when a patient walks in, we can take a simple blood test that tells us if a cancer will spread and also about its molecular signature," she says.
Massimo Cristofanilli, MD, chairman of the department of medical oncology at Fox Chase Cancer Center, is cautiously enthusiastic, saying that a lot more work is needed before either test can be integrated into patient care.
With the CTC chip, he says, one of the issues to be worked out is when to give the test: at the time of diagnosis, surgery, or a few weeks afterward.
There's also the issue of who will pay for new tests, he says. "Insurance will not cover every test for very patient," Cristofanilli tells WebMD.
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Robert W. Veltri, PhD, associate professor of urology and oncology, Johns Hopkins University, Baltimore.
Sunitha Nagrath, PhD, instructor of surgery and bioengineering, Harvard Medical School.
Massimo Cristofanilli, MD, chairman of the department of medical oncology at Fox Chase Cancer Center, Philadelphia.
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