The test could someday be used to answer the most critical question when prostate cancer is diagnosed -- whether the tumor is so aggressive that surgery should be done, or whether watchful waiting will do, said Dr. Arul M. Chinnaiyan.

Chinnaiyan, a professor of pathology at the University of Michigan Medical School, is lead author of a report on the test that appears in the Sept. 22 issue of the New England Journal of Medicine.

"What we are doing is taking advantage of the body's immune system, which ordinarily responds to anything foreign -- viruses, bacteria, cancer," Chinnaiyan said. "As part of that response, the immune system produces antibodies against cancer proteins."

Better Where PSA Is Weakest

Chinnaiyan and his colleagues took samples of DNA from prostate cancer cells and put them into a virus. The cancer DNA produces proteins that differ from the proteins normally found in the body.

The researchers then put the information about 22 of those cancer proteins onto an electronic chip and tested 128 blood samples, 60 from men with prostate cancer, 68 from men without the cancer.

The test did better at detecting prostate cancer than a PSA test conducted on the same samples -- 93 percent accuracy for the new test, compared to 80 percent accuracy for the PSA test, the researchers reported.

"The main point is that this test is not only better, but is better in the area where the PSA test is weakest, at intermediate points of PSA levels," Chinniyan said.

Small Study

The new study was admittedly a small one, so the researchers are moving to confirm the results in a larger number of samples. "We are now extending our work to independent samples from different institutions," Chinnaiyan said. "We are doing pilot tests of samples from around the world."

The test could become widely available "hopefully in a couple of years," he said. "We're trying to push it out of the research laboratory. We are gearing up to function as a reference laboratory. Then we could shift to a commercial provider or develop a chip based on the one we used in this test."

Follow-up studies have to develop a form of the test that could distinguish between fast-growing tumors that require aggressive therapy and those that grow so slowly they pose no death risk, Chinnaiyan said. That test would look for the proteins produced by fast-growing cancers, he said.

Aggressive and Less Aggressive Cancers

Dr. LaMar McGinnis, a senior medical consultant to the American Cancer Society, called the new research "interesting in potential but premature," given the small number of samples reviewed.

"We would welcome some additional help in this most common form of cancer for men," McGinnis said. "The PSA test has been of enormous value in that it enables us to detect prostate cancer at an earlier stage, when it is almost 100 percent curable. The problem is that it is overly sensitive. It does not distinguish between prostate cancers that are aggressive and less aggressive cancers."

But he cautioned that tests based on the same principle used in the new study -- looking for strange immune system antibodies -- "have not been beneficial thus far. Time will tell."

Prostate cancer is the most common type of cancer afflicting American men other than skin cancer. The American Cancer Society estimates there will be about 232,090 new cases of prostate cancer in 2005, and about 30,350 men will die of the disease.

More information: You can learn more about prostate cancer from the American Cancer Society.