Obesity may interfere with prostate cancer screen

NEW YORK (Reuters Health) - The test commonly used to screen men for prostate cancer may be more likely to miss tumors in obese men, a new study suggests.

In a study of 535 men in a free prostate cancer screening program, researchers found that obese men were more likely to have relatively low levels of prostate specific antigen (PSA), even when their prostate findings were abnormal.

PSA levels in the blood typically rise when a man has prostate cancer, so PSA testing is often used to screen for the disease. Men with a high PSA level can then have further testing to get a definitive diagnosis.

The new findings, published in the journal Urology, suggest that because obese men's PSA levels tend to be relatively low in general, some cancers may be missed or not detected promptly.

The generally lower PSA values in heavy men may be the result of a "dilution" effect, according to Dr. Stephen J. Freedland, of Duke University School of Medicine in Durham, North Carolina.

"Obese men have lower PSA values likely due to excess blood volume," Freedland, the senior investigator on the study, told Reuters Health.

"Thus, when interpreting a PSA value in an obese man," Freedland said, "we should adjust the value we call 'abnormal' downwards to reflect this diluted PSA measurement. If we do not, we may be missing cancers in obese men."

Of the men in his team's study, 73 percent were overweight or obese. Compared with their normal-weight counterparts, overweight men had 5 percent lower PSA value, on average. For mildly obese men the difference was 14 percent, and in moderately and severely obese men, the values were 29 percent lower.

"The current data," the researchers conclude, "suggest that the PSA cut-points used to recommend biopsy need to be adjusted for the degree of obesity."

SOURCE: Urology, May 2008.