New Prostate Cancer Test May Detect More Tumors
Thursday, April 26, 2007
An experimental blood test for prostate cancer may help eliminate tens of thousands of unnecessary biopsies at the same time that it detects many tumors that are now missed by the test commonly used, its developers said yesterday.
PSA, the current test, measures a protein normally produced by the prostate, while the experimental one, called EPCA-2, detects a chemical made principally in cancerous tissue.
Prostate cancer, the most common malignancy in men, is one of the more perplexing areas of medicine. Physicians are unsure how to find it and when to treat it.
Today, about 80 percent of prostate biopsies find no tumor -- a percentage that is rising as physicians become more aggressive in searching for the disease.
"We hope this will minimize the number of unnecessary biopsies," said Robert H. Getzenberg, a molecular biologist at Johns Hopkins Hospital who developed the new test, which is still under study and not yet commercially available. A description of it appears today in the journal Urology.
"It's an exciting new marker," said Martin G. Sanda, a urologist at Harvard Medical School. "There certainly is a need for a better test than PSA. Everyone accepts that." His view was echoed by Gerald L. Andriole Jr., chief of urologic surgery at Washington University School of Medicine, who said that "if the data hold up, this marker will be a substantial improvement over PSA."
The PSA test casts a net that is too big and too full of holes. Finding a replacement that catches fewer healthy men, but more of those who do have cancer, would help settle at least one of the clinical conundrums concerning prostate cancer.
The new test is being developed by researchers at Johns Hopkins Hospital and Onconome Inc., a Seattle-based biomedical company. It could become commercially available in 2008.
Prostate cancer is diagnosed in about 230,000 American men each year, and about 30,000 die of it. The death rate is 2.5 times higher among blacks than among whites.
At the moment, men are screened for the disease in two ways -- by a rectal exam and by the PSA (prostate-specific antigen) test. If a lump is detected or if the PSA is above 2.5 (nanograms per milliliter of plasma), most physicians will suggest a biopsy.
EPCA-2 is a protein that is part of the "nuclear matrix," the scaffolding inside a cell's nucleus that helps it copy its genes. The Hopkins researchers measured it in different groups of men whose cancer status was known.
They tried the new test on 30 men with PSA readings above 2.5 and in whom biopsies found no cancer. All had normal EPCA-2 readings (below 30 ng per ml.). This suggested that the test may eliminate many of the "false-positive" PSA results -- readings that are abnormal but apparently do not denote cancer.
On the other hand, the EPCA-2 test appears able to detect cancer even when the tumor is small. It identified 36 out of 40 men who had cancer confined to the prostate gland, and 39 out of 40 men in whom the tumor had spread. It also identified many men -- 14 out of 18 -- who had cancer but whose PSAs were normal.
This last group is especially worrisome to physicians. A study published three years ago found that about 12 percent of men with normal PSA readings have cancer.
The new test is not perfect, though. Getzenberg and his colleagues tried it on 35 men with severe "benign prostatic hypertrophy" -- enlargement of the prostate that sometimes makes the PSA go up but is not cancer. In eight of them, the EPCA-2 was high, suggesting that the EPCA-2 test would flag some men who turn out not to have cancer -- although probably not as many as the PSA test does.
The new test will not help solve the other major clinical uncertainty in prostate cancer. It is unclear who will clearly benefit from aggressive treatment and who are likely to be able to live a normal life if the tumors are simply followed and removed only if they begin to cause symptoms.