The widely used prostate-specific antigen (PSA) test for prostate cancer gives a lot of false positives, resulting in a lot of unnecessary procedures—and worry—for men. So the search is on for a better way to screen for prostate cancer. This week researchers at Johns Hopkins University and the University of Pittsburgh report on a study with a test for a different, recently discovered molecule produced by prostate tumors, called early prostate cancer antigen, or EPCA.

What the researchers wanted to know: How reliable is EPCA as a marker for prostate cancer?

What they did: The researchers got blood plasma from 12 people with prostate cancer and 16 healthy people, as well as six people with bladder cancer, two with colon cancer, one with renal cancer, seven with spinal cord injuries, and two who had been diagnosed with inflamed prostates (but not prostate cancer), a condition that can cause elevated PSA levels. They measured the level of EPCA in all of the patients' plasma with an immunological test. A sample takes on a certain color if it contains EPCA; the more EPCA it has, the deeper the color. Based on a preliminary test on the prostate cancer patients and the healthy people, the researchers set a level of 1.7 absorbance at 450 nanometers (in the indigo range) as their cutoff.

What they found: All but one of the people with prostate cancer scored higher than 1.7 on the EPCA test; of the rest of the people, only two bladder cancer patients had a level higher than 1.7. That means the test did pretty well at pinpointing those with prostate cancer and at ruling out those who didn't have prostate cancer.

What the study means to you: This research could lead to a better way to screen for prostate cancer. But before it's ready for widespread use, the people who make the test will probably tinker with the level that's declared a positive, to set an appropriate balance between missing prostate cancer (false negatives) and telling healthy people they might have prostate cancer (false positives).

Caveats: Not all prostate tumors make EPCA, so a test based on EPCA will never be perfect.

Find out more: The research is funded by Tessera Inc., which hopes to market the test someday.

Learn about prostate cancer from the American Cancer Society.

Read the article: Paul, B. et al. "Detection of Prostate Cancer With a Blood-Based Assay for Early Prostate Cancer Antigen." Cancer Research. May 15, 2005, Vol. 65, No. 10, pp. 4097–4100.

Article online: http://cancerres.aacrjournals.org