Study Finds PSA Test May Miss Most Prostate Cancers

Using a new approach to evaluate test data, scientists from three major medical centers in Boston (MA, USA) have concluded that the prostate-specific antigen (PSA) test may be missing as many as 82% of all prostate cancers. Their findings were reported in the July 24, 2003, issue of The New England Journal of Medicine.

The study, drawn from data on 6,691men who underwent PSA screening and 705 who subsequently underwent biopsy, is based on computer models. First, the data were adjusted for a condition called verification bias and then plotted on a graph that measures the diagnostic capabilities of the test. After comparing the unadjusted numbers to the adjusted ones, the researchers found that selection bias in earlier data had led some researchers to incorrectly assume that PSA screening had near-perfect discriminatory power.

"When adjusting the numbers to account for bias, we discovered that physicians who use a PSA of greater than four (nanograms per milliliter) to recommend biopsy, the current standard, may be missing 82% of cancers in men under 60 years of age and 65% in men over 60,” said Rinaa Punglia, M.D., M.P.H., a radiation oncologist at Dana-Farber Cancer Institute (Boston, MA, USA) and one of the researchers.

The team went on to demonstrate that lowering the threshold to 2.6 in younger men may double the cancer-detection rate, without significantly altering the number of false-positives. No study has yet shown that PSA screening reduces mortality. This study may point to a possible reason, said the team. Other researchers participating were from Brigham and Women's Hospital and Harvard School of Public Health.




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Dana-Farber Cancer Center