http://www.nytimes.com/2005/01/25/health/25test.html
VITAL SIGNS
Testing: Obesity May Skew Prostate Test
By JOHN O'NEIL
Published: January 25, 2005
besity appears to skew the results of the most common test used to
detect prostate cancer, a study released yesterday concluded.
According to the study, which was released online and will be published
in March in the journal Cancer, earlier research has shown that obese
men have a lower survival rate for prostate cancer and that their cancer
tends to be diagnosed in more advanced forms.
The researchers, led by Dr. Ian Thompson of the University of Texas
Health Science Center in San Antonio, wondered whether obesity might in
some way throw off the results of testing for prostate specific antigen,
or P.S.A., a blood protein used to identify the disease in its early
stages.
They examined samples from 2,779 men, none of whom had prostate cancer.
They found that the P.S.A. levels indeed changed with weight: after
adjusting for race and age, both of which affect P.S.A. levels, they
found that men with body mass index levels of 40 or above had readings
one-third lower than men whose weight was normal.
"This suggests that P.S.A. is being suppressed, which may be delaying
diagnosis in obese men," Dr. Thompson said.
Dr. Thompson said that a P.S.A. reading of 4 or above used to be
considered a hard-and-fast trigger for further testing for the disease,
but that the picture had become more fluid recently because of the
discovery that many cancers could be found at lower P.S.A. levels.
He said that if the study's findings were validated, obesity might take
its place, along with factors like family history of cancer, in a
physician's decision to act more aggressively in following up on a
P.S.A. result.