Dec 12 2005
According to a new study a prostate cancer-screening test may not be that reliable.
The study reveals that the test may be compromised by lifestyle and demographic factors, and that the concentration of prostate specific antigen (PSA) over time, the PSA velocity, can be significantly affected by age, race, and diet, leading to falsely lower or elevated values and possible misinterpretation by doctors.
Study co-author Dr. Ian M. Thompson, of the department of urology at the University of Texas Health Science Center at San Antonio, says that unlike PSA, PSA velocity has not been so scrutinised, and the velocity appears to be affected more by lifestyle variables.
Other studies have shown a decrease in prostate cancer deaths 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.
PSA blood tests screen for abnormally high levels of PSA, which can indicate the risk of new or recurring prostate cancer.
While investigators continue to refine the test, there is little 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.
They found that PSA velocity was significantly affected by age, race and diet, potentially affecting its clinical interpretation.
PSA velocity decreased as men aged, and increased with high 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 and men who gained weight had lower PSA velocity and those who lost weight had higher PSA velocity.
As in other studies, it was found that PSA concentration increased with age and decreased with obesity.
The authors say that although 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.
They say that race, smoking, age, energy intake, calcium supplement use and weight change were associated with substantial differences in PSA velocity, and a doctor could be biased by these factors.
The American Cancer Society recommends that healthy men aged 50 and older undergo yearly PSA blood tests, along with a digital rectal exam.
The study is published in the January 15, 2006 issue of CANCER.