New
model predicts likelihood of prostate cancer prior to biopsy
Oregon
Health & Science University
Public
Release:
August 25, 2003
Using
easily accessible data, model could reduce unnecessary prostate biopsies
by 24 percent
PORTLAND,
Ore. -- A new, simple predictive model
could reduce the number of unnecessary prostate biopsies by 24 percent
without sacrificing cancer detection, according to a study to be published
in the Oct. 1 issue of CANCER and available online beginning Aug. 25 at
the Wiley InterScience Web site.
"While
current prostate cancer screening practices are good at helping us find
patients with cancer, they unfortunately also identify many patients who
don't have cancer. Three out of four men who receive a prostate biopsy
after an abnormal prostate screening test do not have cancer at all,"
said Mark Garzotto, M.D., principal investigator, member of the OHSU
Cancer Institute and director of urologic oncology at the Portland
Veterans Affairs Medical Center. "So the challenge has been to
develop a model that both predicts which men will have prostate cancer and
spares men without prostate cancer from unnecessary biopsies."
Prostate
cancer is the most common cancer in men and the second leading cause of
cancer-related death in American men. Overall, roughly one in six men will
develop prostate cancer during his lifetime. Prostate biopsy can be a
source of patient discomfort, bleeding and infection, and can burden the
health care system with extra costs.
This
new model -- a nomogram -- predicts the detection of prostate cancer in
men with a prostate specific antigen (PSA) level of less than or equal to
10 ng/ml. Prostate cancer screening using a PSA test has been associated
with a decline in prostate cancer deaths in the United States.
About
10 percent of men who are tested will have an elevated PSA. However, PSA
becomes specific only when it exceeds 10 ng/ml. When the PSA is modestly
elevated from 4 to 10 ng/ml, which it is in the majority of cases, it is
associated with cancer in about 25 percent of men who are biopsied.
Attempts to develop predictive models for PSA values less than 10 have
been made, but to date they have been unable to identify low-risk groups
that do not need prostate biopsy.
"Our
model accurately predicts prostate cancer in men whose PSA level is below
10 ng/ml, a level at which the PSA test can't tell us who doesn't have
cancer," Garzotto said.
The
nomogram is based on easily accessible laboratory, clinical and
transrectal ultrasound (TRUS) data. The nomogram itself is a graphic made
up of lines representing individual risk factors marked off to scale and
arranged in such a way that a numeric representation of the likelihood of
cancer can be easily calculated. For example, a total score of 6.8
corresponds to a 10 percent likelihood of positive prostate biopsy.
In
developing the nomogram, study authors identified independent risk factors
associated with malignant biopsies. The data revealed four independent
predictors of a positive biopsy: elevated PSA density, abnormal digital
rectal exam, abnormal/hypoechoic transrectal ultrasound and age greater
than or equal to 75. Patients younger than 75 with normal DREs, normal
TRUS and normal PSAD of less than 0.09 had a less than 5 percent chance of
having malignancy on biopsy and, therefore, were low-risk patients. A
patient aged 75 years or older who had an abnormal DRE, abnormal/hypoechoic
TRUS and an abnormal PSAD value of 0.30 had a 59 percent chance of having
prostate cancer.
"Not
only could this model reduce unnecessary biopsies, it could be a useful
tool in preparing patients for possible outcomes before the biopsy,"
said Garzotto, who posted a copy of the nomogram in his clinic next to the
ultrasound machine, where he finds it most useful.
###
Study results are available
via Wiley InterScience at http://www.interscience.wiley.com/cancer
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