Prostate cancer test affected by demographic and lifestyle factors

The reliability of a prostate cancer-screening test may be compromised by lifestyle and demographic factors, according to a new study. Published in the January 15, 2006 issue of CANCER, a peer-reviewed journal of the American Cancer Society, the study reveals the (rate of) change in concentration of prostate specific antigen (PSA) over time–a calculation called PSA velocity–can be significantly affected by age, race, and diet, leading to falsely lower or elevated values and possible misinterpretation by doctors. Single determinations of PSA concentration, the most common use of the PSA screening test, were minimally but significantly affected by age and body mass index (BMI).

Studies have shown a decrease in prostate cancer mortality since 1992 and some researchers attribute a portion of that fall to the widespread adoption of the PSA test. But some experts say that PSA concentration alone causes too many false positives and leads to many unnecessary tests, such as biopsies and transrectal ultrasounds. Investigators continue to refine the test, including developing calculations such as PSA velocity, PSA density, and age-specific PSA, or other tests such as percent free PSA. However, there is poor understanding of the effect of other factors, such as diet, race, and weight on PSA and its related measurements.

Alan R. Kristal, Dr.P.H. of the Fred Hutchinson Cancer Research Center in Seattle and colleagues reviewed PSA and PSA velocity data from 3,341 cancer-free men to determine relationships between PSA tests and demographic and lifestyle factors.

PSA velocity was significantly affected by age, race and diet, potentially affecting its clinical interpretation. PSA velocity decreased as men aged, and increased with higher total energy (calorie) diets. PSA velocity in African Americans was on average almost twice the level of Caucasians, and was lower among users of high-dose calcium supplements. Large weight fluctuations also affected PSA velocity. Men who gained weight had lower PSA velocity and those who lost weight had higher PSA velocity.

As was found in other studies, single determinations of PSA concentration increase with age and decrease with obesity. These differences, while statistically significant, were considered minimal and would have little influence on clinical interpretation of PSA value.

While the authors considered the impact of demographic and lifestyle factors on the clinical interpretation of a single PSA concentration was negligible, the clinical impact on interpreting PSA velocity was considered significant. “Race, smoking, age, energy intake, calcium supplement use and weight change were associated with substantial differences in PSA velocity,” they conclude, “and clinical interpretation of PSA velocity could be biased by these factors.”