Risk of aggressive prostate Ca underestimated by diagnostic tool

An Internet-based formula often used by physicians to calculate a patient’s prostate cancer risk systematically underestimates the probability that the patient may have an aggressive form of the disease, say researchers from the Stanford University School of Medicine, Stanford, CA.

The Prostate Cancer Risk Calculator (PCRC) does a reasonably good job of predicting the overall likelihood of a patient having prostate cancer, said Joseph Presti Jr, MD, the study’s senior author. But the PCRC underestimates the odds that a patient who is a candidate for referral to a urologist for suspicion of prostate cancer will test positive, on biopsy, for a high-grade tumor, he said.

"That’s just the kind of prostate cancer you want to detect as soon as possible," said Dr. Presti.

In the study, which was published in the Journal of Urology (2011; 185:483-7), Dr. Presti and colleagues applied the statistical formula used to generate the PCRC to a more recent sample called the Stanford Prostate Needle Biopsy Database. This database consisted of 636 men of all ages, never previously biopsied, who had been referred to Stanford urologists for suspicion of prostate cancer. All patients received a 12-core needle biopsy.

The team found that the actual risk of having high-grade prostate cancer was approximately double the risk predicted by the PCRC.

The danger of relying on the PCRC, Dr. Presti said, is that a patient who should get biopsied will develop a false sense of security because he’s been led to believe his risk of an aggressive tumor is lower than it really is. Believing that the risk doesn’t justify the inconvenience and, in some cases, the cost of a biopsy, the patient may then decide against undergoing the procedure.