Extra Weight Skews PSA Scores

MONDAY, Jan. 24, 2005 (HealthDayNews) -- Extra weight makes it harder for doctors to detect prostate cancer.

That's the conclusion of a study appearing in the March 1 issue of Cancer, which found that a higher body mass index (BMI) was associated with lower prostate specific antigen (PSA) levels. Higher PSA scores often point to prostate cancer.

"Obesity affects PSA levels, and causes them to be decreased," said study co-author Jacques Baillargeon, an associate professor of epidemiology at the Center for Epidemiology and Biostatistics at the University of Texas Health Science Center at San Antonio.

These findings may help explain why overweight men have been found to have an increased risk of death from prostate cancer in previous studies.

"[Higher BMIs} may have caused delayed disease ascertainment, which means men are being diagnosed at a later stage, when they may have more aggressive disease," Baillargeon explained.

Prostate cancer is extremely common in older men, and is the second deadliest form of cancer for American men, reports the National Prostate Cancer Coalition. The American Cancer Society estimates that more than 30,000 men in the United States will die from prostate cancer this year and that more than 230,000 new cases will be diagnosed this year.

Because early prostate cancer generally shows no symptoms, doctors rely on two screening tools, the PSA test and digital rectal exams. However, the PSA has recently come under fire because some studies have suggested the test misses many cancers.

Dr. Ian Thompson, lead author of the current study and the author of one of the studies that found PSA tests were missing some cancers, said that some reports of the previous results may have made it look like the test is ineffective.

But, he added, that is not the case.

"As a cancer-screening test, PSA is remarkably good," said Thompson, adding that the results of the test are not black and white. "PSA functions like blood pressure or cholesterol screenings: the higher in the range, the higher the risk. If you have a very low PSA, your risk is low, but not nonexistent. Can you have a heart attack with low cholesterol? Yes. Can you have high cholesterol and smoke and live to 95? Sure."

But, those scenarios are the exception rather than the rule, according to Thompson, who is chairman of urology at the University of Texas Health Science Center at San Antonio.

And, he said, "PSA gives you a good handle on your risk."

The current study, said Thompson, showed that obesity and other factors that modify PSA "should probably be taken into account when you evaluate a man's risk of prostate cancer."

Thompson and his colleagues tested the PSA levels of almost 2,800 men who didn't have prostate cancer. They measured the mens' height and weight and gathered information on race, age and lifestyle factors, such as dietary habits and supplement use, according to Baillargeon.

They found that regardless of age or race, when BMI went up, PSA levels decreased.

BMI is a measure of your body fat, found by using your height and weight measurements. The higher the BMI, the more body fat you have. A BMI above 30 is considered obese.

The authors said they don't know exactly why higher BMIs would affect PSA scores, but they suspect that PSA is suppressed in heavier men because obese men have lower levels of testosterone. According to Thompson, PSA production is sensitive to testosterone levels.

"Lower testosterone may be artificially lowering PSAs, and may be delaying diagnosis. That delay may be why obesity is associated with a higher risk of mortality after treatment," Thompson said.

Dr. Christopher Lee, an urologist at New York University Medical Center, said this study "tells us for sure what we had suspected all along is true. Obese men could have lower levels of PSA than the general population. This study suggests that if you are obese, perhaps we should look at lower levels of PSA with more scrutiny, and perhaps [you should] be more aggressively pursued in terms of having another PSA test or biopsy."

Thompson added that someone who is at high risk of prostate cancer because of family history, increasing age or because they are black, should think about seeing a urologist for prostate cancer screening.

More information

To learn more about prostate cancer, visit the American Cancer Society.