Categorized | Feature, Prostate Health

Online Prostate Cancer Tool May Be Inaccurate

The popular online prostate cancer tool has recently come into scrutiny. The tool, called the Cancer Risk Calculator for Prostate Cancer, is sometimes used by some clinicians to determine the risk of prostate cancer for patients. However, a Stanford University study, published online December 20 in Urology, found that the tool underestimates the probability that a patient may have an aggressive form of the disease.

The risk calculator is used by a “wide range of individuals, including patients, primary care physicians and urologists,” writes the study authors, led by Tin Ngo, MD, a urology resident at Stanford in Palo Alto, California.

The risk calculator works by incorporating the variables of race, age, prostate-specific antigen (PSA) level, family history, digital rectal exam, prior prostate biopsy, finasteride use, body mass index, and PCA3, a newer urinary measure. After the user inputs this information, the calculator determines a level of risk for biopsy-detectable prostate cancer.

However, the calculator underestimates high-risk disease, which leads to a failure of accurately estimating “just the kind of prostate cancer you want to detect as soon as possible,” said senior author Joseph Presti, Jr., MD, professor of urology, in a press statement.

“[The risk calculator] is not a perfect determinant of risk and should not be used as such,” says Stephen Eyre, MD, in an editorial accompanying the new study. “The calculator is to be used as a guide toward risk stratification.”

Ian Thompson, MD, one of the developers of the risk calculator, defended the tool and emphasized its positives.

“The risk calculator has repeatedly been validated in multiple external populations and…substantially improves on the assessment of a man’s risk of prostate cancer over just using PSA alone,” said Dr. Thompson. He continues, “The primary point of the calculator is that physicians cannot use PSA alone as they oftentimes do.” Clinicians need to incorporate other risk factors in the decision about performing a prostate biopsy, he added.

Dr. Thompson also suggested the new study’s findings were not outside the realm of possibility, given the fact that the Stanford investigators used a “fundamentally different” population of men in their assessment of the accuracy of the calculator than originally used to develop the risk calculator.

A disclaimer is also provided on the calculator’s Website and suggests its results are neither final nor perfect: “This calculator is designed to provide a preliminary assessment of risk of prostate cancer…Additional clinical information may modify this risk.”

Further, Dr. Thompson explained that the calculator is not quite finished. “We are constantly improving the calculator (and have recently included body mass index and the PCA3 urinary prostate cancer detection test), and so it will improve with time,” he said.

The authors of the new study explain that they used a different population of men because the sample that was used to develop the risk calculator was not representative. The sample of men formerly used does not represent the typical man referred to an urologist for risk assessment and possible prostate cancer biopsy. “Referred” men have a higher risk for prostate cancer, they say.

Instead, the Stanford study authors decided to use the risk calculator to assess men from the Stanford Prostate Needle Biopsy Database, all of whom were referred to Stanford urologists for suspicion of prostate cancer and were biopsied.

When the Stanford investigators crunched their own numbers using their data, they found that their “predictions of overall prostate cancer risk did not differ significantly from those of the calculator.” However, they stated, “Our model predicted a much greater risk of high grade disease than the prostate cancer risk calculator.”

“The difference between our estimated risk of high grade prostate cancer and that of the prostate cancer risk calculator can be potentially explained by 1) differences between the cohorts (referred vs. unreferred) or 2) the difference in grading, i.e. grading accuracy due to the difference in biopsy schemes or to temporally related grade shifts,” write the authors.

With regard to the second point, the authors note that biopsy schemes have largely changed in urology practices since the PCPT study was started, which may weaken the usefulness of the calculator.
“Since most biopsies done in PCPT were sextant, the validity of PCRC [the calculator] predictions in contemporary patients, of whom most undergo 12-core biopsy, is unclear,” they write.

2 Responses to “Online Prostate Cancer Tool May Be Inaccurate”

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