August 26, 2003 (USA TODAY) -- Performing a simple set of calculations for men who have abnormal PSA tests could help up to 24% of these men avoid an unnecessary biopsy of the prostate gland, a study suggests today.
More than 1 million men a year have biopsies of the prostate gland after a cancer-screening test reveals moderately elevated levels of prostate specific antigen (PSA) in the blood. Half of men over age 50 have PSA blood tests.
The problem is that only one in four of these biopsies finds evidence of cancer, says Mark Garzotto, director of urologic oncology at the Portland Veterans Affairs Medical Center and a researcher at the Oregon Health & Science University Cancer Institute.
"Typically when a patient walks through the door with an elevated PSA, his individual chance for cancer is 25%," Garzotto says. "We tend to biopsy all comers, which does not take into account individual variations that cause an elevated PSA."
Experts estimate that 750,000 of the 1 million biopsies performed each year are unnecessary. The most common reason for an elevated PSA is benign prostate enlargement, which is normal in older men.
Garzotto and his colleagues studied more than 1,200 men with PSA levels ranging from 4 to 10 (0 to 3 is considered normal) who had biopsies from 1993 to 2000. They found that the most important predictors of cancer were:
- A digital rectal exam to feel for a hardened nodule that may be a tumor.
- A transrectal ultrasound to look for a darkened area that may be cancerous.
- A man's age: 90% of prostate cancer cases are in men over 65.
- PSA density, which is the ratio between PSA level and prostate size. A smaller gland with elevated PSA is more likely to be cancerous than a larger gland with elevated PSA.
When patients were given points on these criteria using a mathematical model called a nomogram, researchers could predict which men had the lowest odds of having cancer.
A nomogram uses bits of information, such as specific risk factors or clinical test values, to arrive at a statistical probability for a particular outcome. Urologists already use nomograms to predict whether positive biopsy tissue represents a more aggressive tumor or a less aggressive one.
Garzotto said his group's nomogram, which is reported today in the online edition of Cancer, could reduce unnecessary biopsies by about 200,000 cases a year.
Michael Manyak, director of urology at George Washington University Medical Center, calls the study promising. "Anything we can do to avoid unnecessary procedures is commendable. The question is will the data hold up with newer biopsy procedures in which more tissue is sampled," Manyak says.
During the study period, urologists routinely took about six cores of tissue from the prostate gland. Manyak says taking 12 samples is more accurate.
Garzotto says he analyzed a subgroup of patients in which at least 10 to 12 samples were taken per biopsy procedure, but he found no difference in the predictive value of his mathematical model. His group has added 500 patients since finishing the study and continues to analyze the data.
Copyright 2003 USA TODAY, a division of Gannett Co. Inc.
