FRIDAY, Aug. 8, 2008 (HealthDay News) -- The standard screening test for prostate cancer may not be accurate for obese men, leaving them more vulnerable to the disease, and surgery is less likely to be effective for them, a new pair of studies found.
"Obese men are more likely to be diagnosed with an aggressive form of the disease," said Dr. Stephen Freedland, an associate professor of urology and pathology at the Duke University Prostate Center, and an author of one of the studies.
The reason: The blood test that looks for elevated levels of the protein prostate-specific antigen (PSA), indicating a heightened cancer risk, doesn't seem as reliable for obese men, Freedland said.
"Our assumption is that these men have more blood volume, so PSA gets diluted, he said. "By the time obese men get to elevated levels, the cancer is more advanced."
The study, published online Friday in the journal BJU International included nearly 3,400 men who had PSA tests. The researchers found that the risk of an aggressive cancer was doubled in obese men diagnosed because of high PSA levels. No such association was found for obese men diagnosed by a digital rectal examination, in which the physician feels for an abnormally large prostate gland.
Prostate cancer is suspected when the PSA reading is 4 or higher. The current recommendation is for men aged 50 and older to be offered an annual PSA test, with explanations of its possible risks and benefits. A federal preventive medicine committee this week said that PSA screening should not be done for men aged 75 and older because the risks outweigh the benefits.
"I'm not sure that we should check obese men more often," Freedland said. "But we should have a higher [PSA] index of suspicion of what is not normal -- 3.4 rather than 4; for really obese men, 3.2."
The Duke study measured obesity using body-mass index, which is a ratio of weight to height. Obesity is defined as a BMI of 30 or more.
A second report from Duke in the same issue of the journal found that excess weight influenced the outcome of surgery for prostate cancer. Men with a BMI of 35 or higher were nearly 60 percent more likely to have a recurrence of the cancer than thinner men, the study of 1,434 men found.
One reason is "the difficulty of operating on obese men in general," said study author Dr. Jayakrishnan Jayachandran, a urology oncology fellow at the Duke Prostate Cancer Center. "The prostate is a narrow thing to operate on, and when there is a big wad of fat in your way, if the abdominal wall is thick, it becomes a technical issue."
The result is that not all the cancer may be removed, which means a recurrence after time, Jayachandran said. "The only thing we can think of is that when you operate on obese people, you have to be more careful," he said.
The studies results apply to men who might not regard themselves as obese, Freedland said. "We can't forget that when we use the term, we are not just talking about very large men," he said. "A man who is 5 foot 9 and weighs 203 pounds would be considered obese."
Jayachandran added, "We are not screening these obese men effectively and are not doing as good a job surgically as could be done."
To learn more about prostate cancer, visit the U.S. National Cancer Institute.