A man’s age, race and diet have a significant impact on how much his prostate-specific antigen (PSA) concentration changes over time, according to a report released Dec. 12 by researchers from institutions including the Health Science Center and the Cancer Therapy and Research Center (CTRC).
PSA is the subject of scrutiny in the medical community. Some say that while the test finds most serious-grade tumors, false-positive readings cause many men whose tumors are not destined to be life threatening to undergo unnecessary invasive tests and treatment, sometimes resulting in impotence and/or incontinence.
The new research, led by Alan R. Kristal, Dr.P.H. of the Fred Hutchinson Cancer Research Center in Seattle, examined PSA data from 3,341 cancer-free men to uncover linkages between PSA tests and demographic and lifestyle factors.
“Dr. Kristal’s study expands upon work that was begun here in San Antonio by the prostate researchers at the Health Science Center in a project led by Dr. Jacques Baillargeon,” said Ian M. Thompson Jr., M.D., professor and chairman of the department of urology at the Health Science Center. “In almost 3,000 men who are participating in the San Antonio Center of Biomarkers of Risk (SABOR) program, Dr. Baillargeon was the first scientist to report that as a man’s weight increases, his PSA decreases.
“It was previously thought that prostate cancers were more aggressive in obese men. Now we think the explanation is simply that hormonal changes that occur with obesity prevent PSA from increasing as prostate cancer develops. Obesity thus seems to hide cancers until later, when they may be more aggressive. Our work with Dr. Kristal expands on this observation, and it shows that other behavioral factors, including diet and supplement use, can also affect how PSA changes over time.”
The new study is based on data from men enrolled in the Prostate Cancer Prevention Trial, a seven-year U.S. trial that showed men who received the drug finasteride vs. placebo had a 25 percent reduced risk of developing prostate cancer.
Many physicians, trying to improve on how PSA detects prostate cancer, have begun to rely on the rate of increase of PSA to determine when to conduct further investigations such as a prostate biopsy. “This study shows that these changes in PSA may be related as much to behavioral factors, including weight change and caloric intake, as to risk of cancer,” Dr. Thompson said. “We are just not sure if change in PSA, as a measure, is better than simply the PSA value itself.”
Karen Fields, M.D., president and chief executive officer of the CTRC, said the new data “raise important questions about the interactions between PSA screening, lifestyle and other demographic data. It is critical that clinical trials such as this be evaluated to give clinicians high-quality information not only to screen patients, but to advise and intervene with rational strategies to decrease the risks of prostate cancer and its precursors.”
Is this a step backward for the prostate-specific antigen test?
“Some people may say that this is a failing of PSA,” Dr. Thompson said. “I’d rather look at it as helping us make the test even more accurate. We are working on ways for patients and their doctors to incorporate all of these factors into a method whereby instead of monitoring PSA, we monitor actual risk of prostate cancer. I think that’s what modern medicine is seeking.”
Thomas J. Slaga, Ph.D., professor of pharmacology at the Health Science Center, added: “These recently reported clinical studies are very important to better understand limits of the PSA assay in order to more accurately determine the risk to prostate cancer.”
The results will be published in the Jan. 15, 2006, issue of CANCER, a peer-reviewed journal of the American Cancer Society. The journal made the results available online Dec. 12.
Drs. Fields, Thompson and Slaga are members of the San Antonio Cancer Institute, one of the two National Cancer Institute-designated Cancer Centers in Texas. The San Antonio Cancer Institute is a partnership of the Health Science Center and CTRC.