The test for elevated levels of prostate-specific antigen (PSA) to detect prostate cancer appears to be biased against obese men, whose PSA levels tend to be deceptively low, say researchers from the Duke University Prostate Center. This bias, they explain, may be creating more aggressive cancers by delaying diagnosis. "We know that obese men tend to have lower PSA values than their normal-weight counterparts, possibly caused by larger blood volumes which dilute the readings," said Duke urologist Stephen Freedland, who led the research. "Now we know some of the real implications of this - that these men are at a disadvantage in terms of prognosis compared to normal-weight men."
Freedland's team used patient data to examine the association between body mass index (BMI) and the amount of disease discovered after surgery to remove the prostate. "We compared men who had their cancers detected by PSA screening to those who had an abnormal digital rectal exam, which may not confer the same bias against obese men," Freedland said.
The researchers looked at a total of nearly 3,400 men and found that obese men whose cancer was diagnosed by PSA testing had more than twice the risk of cancer recurrence after surgery than their normal-weight counterparts. "In contrast, obese men with abnormal digital rectal exams had similar outcomes as normal-weight men," Freedland explained.
The researchers are hopeful that this data, coupled with the earlier data on which it builds, may be a catalyst to encourage alternative screening methods for obese men, or a lower threshold for worrisome PSA levels in obese men. "Obesity is very common in the United States, so this potentially affects a lot of people," Freedland said. "We can't forget that when we use the term obese we are not just talking about very, very large men. A man who is 5 foot 9 and weighs 203 pounds would be considered obese."
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Source: Duke University Medical Center
