Gen-Probe Prostate Cancer Test Looks Promising

6/9/10

Gen-Probe (NASDAQ: GPRO) appears to be on the right track with its experimental prostate cancer test, judging from a raft of recent clinical studies in men being screened for prostate cancer.

The research, presented at the annual meeting of the American Urological Association in San Francisco last week, provided additional evidence that Gen-Probe’s PCA3 urine test might help eliminate the need for additional biopsies in men with positive PSA tests.

The PSA, or prostate specific antigen test, is the primary screening test for prostate cancer. Because the test has a high false-positive rate, men must undergo biopsies, a painful procedure in which prostate tissue is taken for analysis, to confirm the presence of cancer.

Men with positive PSA test results and negative biopsies have a dilemma. “The PSA said they have cancer but their doctors can’t find it,” said Gen-Probe spokesman Michael Watts. If these patients continue to test positive on a follow up PSA, they face a second biopsy, he said.

Gen-Probe’s PCA3 test has a relatively low false-positive rate, so it could be used to assess the need for a second biopsy. A high score might indicate a biopsy was needed, whereas a low score might indicate a low risk of aggressive cancer, making a second biopsy unnecessary.

In one key study presented at the meeting, the PCA3 was used to analyze urine samples from 1,946 men. Results showed that a positive PCA3 was a more reliable indicator of cancer than a positive PSA. Seventy-eight percent of men with positive PCA3 results had cancer versus 21 percent of men with positive PSA scores.

The study confirmed the PCA3 has a high-false negative rate, which is why it is not seen as a replacement for the PSA. Just 49 percent of men with a negative PCA3 were cancer-free versus 87 percent of men with negative PSA scores.

As I previously reported, the PCA3 test detects genetic material from the PCA3 gene, which is 65 times more common in prostate cancer cells than normal cells.

Gen-Probe has completed enrollment in a 500-patient pivotal study that will determine whether the PCA3 test can reliably predict which men need a second biopsy following a first negative biopsy and positive PSA result. The company expects to have the results in time to submit a marketing application for the device to the FDA in the third quarter, Watts said. The test, which is available in Europe, could reach the U.S. market in 2011.

Denise Gellene is a former Los Angeles Times science writer and regular contributor to Xconomy. You can reach her at dgellene@xconomy.com Follow @

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