Assessing need for repeated biopsies.

Researchers at the Washington University School of Medicine have developed a formula designed to boost the diagnostic power of the prostate-specific antigen (PSA) blood test, the most sensitive screening tool available for prostate cancer. The PSA density formula may help physicians decide how aggressively to re-biopsy men who end up in diagnostic limbo--those whose PSA tests identify them as cancer candidates, but whose biopsies do not reflect a tumor.

The test, used to detect prostate cancer, the second-leading cause of cancer deaths in American men, measures the level of the PSA protein, produced only in the walnut-shaped prostate gland. PSA is a component of semen that thins the liquid to help sperm swim through it. Above-normal levels are an indication of prostate disease, explains Gerald L. Andriole, associate professor of urologic surgery.

The test is not foolproof, since not every man with elevated PSA has cancer. High levels of the protein also can be a sign of benign enlargement of the prostate. Physicians rely on biopsies to tell the difference. They recommend biopsies for patients with PSA values of four micrograms per liter or higher. "If PSA levels are elevated, we often recommend having a prostate gland biopsy. What we find is that two-thirds of the biopsies do not show cancer. Then we're faced with a dilemma: Is there no cancer, or did we just miss it?"

Biopsies can fail to detect cancer because they are limited to testing only a tiny portion of the organ suspected to be in trouble. A small sample is removed from the organ, then magnified and examined for the presence of malignant cells. However, that sample does not always reflect the health of the entire organ. "If the cancer is very small and the prostate is very large, it's easy to imagine that the needle might not find the cancer."

Because of the possibility of undetected cancer, some men are caught in an unpleasant cycle, having to repeat the uncomfortable biopsy procedure every six months as long as their PSA levels remain high. Some have as many as six over time...

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