New Model Predicts Likelihood of Prostate Cancer Prior to Biopsy
08/25/03 Portland, Ore.
Using easily accessible data, model could reduce unnecessary prostate biopsies by 24 percent
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 beginning Aug. 25.
Mark Garzotto, M.D., is an assistant professor of surgery (urology) in the OHSU School of Medicine, director of urologic oncology at the Portland Veterans Affairs Medical Center, and a member of the OHSU Cancer Institute.