Obesity may affect accuracy of prostate screening

Researchers say obesity is associated with lower prostate specific antigen (PSA) levels in men, making the screening test likely to produce unreliable results in this population. The full study is published in the March 1, 2005 issue of CANCER (http://www.interscience.wiley.com/cancer-newsroom), a peer-reviewed journal of the American Cancer Society.

Since the use of early detection tests for prostate cancer became relatively common (about 1990), the prostate cancer death rate has dropped. But it is still unclear whether the drop is a direct result of screening. Studies are underway to try to determine if early detection tests for prostate cancer in large groups of men will lower the prostate cancer death rate.

Obesity, defined as a body mass index (BMI) over 30, is a growing public health issue in the U.S., and is associated with chronic diseases such as diabetes. A landmark American Cancer Society study in April 2003 added prostate cancer to the list of cancers linked to an unhealthy body weight, with men at the highest BMI at 34 percent higher risk. Studies also show obesity is associated with poor prognostic association as well. Obese men with prostate cancer are diagnosed at more advanced stages and have higher mortality rates. Hypotheses include tumorigenic links to elevated hormones, such as estrogen and insulin-like growth factor.

Another hypothesis states that obesity may actually make available screening tests insensitive. In order to test this hypothesis, Jacques Baillargeon, Ph.D. of the University of Texas Health Science Center in San Antonio and colleagues investigated the association between BMI and PSA levels in 2779 men without prostate cancer in a study sponsored by the Early Detection Research Network of the National Cancer Institute.

The researchers found that as BMI increased, PSA linearly decreased. This finding was consistent regardless of age and race.

These findings, the authors conclude, may explain “the recent reports of inferior outcomes of prostate cancer treatment in obese men” in that they “may be caused by delayed detection” rather than biological differences in the tumor. The study implies that physicians may consider adjusting PSA values when screening for prostate cancer if men are overweight or obese.