US scientists are hopeful that a blood test for a newly discovered protein will vastly increase the reliability of screening for prostate cancer. The protein is called early prostate cancer antigen-2 (EPCA-2).
The study is published in Urology and was led by Robert H Getzenberg, professor of urology and director of research at the James Buchanan Brady Urological Institute at The Johns Hopkins University School of Medicine in Baltimore, Maryland.
Prostate cancer is the most common cancer in American men. According to the American Cancer Society, over 200,00 new cases of the disease will be found in the US in 2007, and over 27,000 men will die from it.
The current blood test for prostate cancer looks for another blood protein called prostate-specific antigen (PSA). If PSA is above a certain level (2.5 nanograms per milliliter), men are referred for biopsy to verify presence of cancerous cells.
However, there are three problems with the PSA based test:
(1) It has a high level of false positives: most of the biopsies come back normal. According to Prof Getzenberg, 80 per cent of the 1.6 million men referred for prostate biopsy in the US every year return negative results.
(2) It has a high level of false negatives as well: it fails to find prostate cancers that have a low level of PSA. Prof Getzenberg suggests that 15 per cent of men with prostate cancer go undetected because their PSA level is below the cutoff.
(3) It can’t tell if the cancer has spread to other parts of the body.
The researchers reckon their new test will improve prostate cancer screening and testing on all three counts.
Prof Getzenberg said in a prepared statement:
“A blood test based on EPCA-2 may greatly improve our ability to accurately detect prostate cancer early and minimize the number of false positives, therefore lowering the number of unnecessary biopsies.”
“This is the first time we have a test that effectively distinguishes between men with cancer confined to the prostate and those whose disease has spread outside of the gland,” he added.
The researchers tested the blood of 330 Hopkins patients for EPCA-2 levels. The patients were grouped as:
— Men with normal PSA who had prostate cancer.
— Men with normal PSA who did not have prostate cancer.
— Men with elevated PSA but negative biopsies.
— Men with a noncancerous prostate condition called benign prostatic hypertrophy (BPH) who did not have biopsies.
— Men with prostate cancer that had not spread.
— Men with prostate cancer that had spread elsewhere.
— Patients with benign conditions of other organs.
— Patients with other types of cancer.
They used a cut off level of 30 nanograms of EPCA-2 per milliliter. They settled on this level after doing a pilot study of 30 blood samples.
The results showed that:
— The EPCA-2 test detected 97 per cent of the patients who did not have prostate cancer.
— Men with no evidence of the disease (regardless of their PSA level) had EPCA-2 levels below the cutoff.
— Patients with other types of cancer and benign conditions also had EPCA-2 levels below the cutoff.
— The EPCA-2 test detected 94 per cent of the men with prostate cancer.
— 90 percent of the men with organ-confined prostate cancer had EPCA-2 levels at or above the cutoff.
— 98 percent of the men with disease outside the prostate also had EPCA-2 levels at or above the cutoff.
The results also showed that 77 per cent of the patients with BPH had EPCA-2 levels below the cutoff, which the researchers say is within the likely percentage rage of BPH patients who do not have prostate cancer. This is a particularly encouraging result, they said, because patients with BPH often have elevated PSA which results in misdiagnosis and unnecessary biopsies.
Also, the EPCA-2 levels for prostate cancers that had spread were significantly higher than for those that had not. The test was dramatically better at separating these groups, the researchers found.
Prof Getzenberg said:
“This is important, since cancer that has spread outside the prostate is more deadly, which makes it even more crucial to have a tool that detects it early.”
The researchers concluded that:
“The results of our study have shown that EPCA-2 is a novel biomarker associated with prostate cancer that has high sensitivity and specificity and accurately differentiates between men with organ-confined and non-organ-confined disease.”
Larger clinical trials for EPCA-2 are currently being planned, and the scientists hope this could make the test available to the public in approximately 18 months.
The study was funded by the National Cancer Institute of the National Institutes of Health, and Onconome Inc, a company that employs Prof Getzenberg as a consultant. Prof Getzenberg will also receive royalties from the product.
“EPCA-2: A Highly Specific Serum Marker for Prostate Cancer.”
Eddy S. Leman, Grant W. Cannon, Bruce J. Trock, Lori J. Sokoll, Daniel W. Chan, Leslie Mangold, Alan W. Partin and Robert H. Getzenberg.
UrologyVolume 69, Issue 4, April 2007, Pages 714-720.
doi:10.1016/j.urology.2007.01.097
Written by: Catharine Paddock
Writer: Medical News Today