“Direct to consumer” testing for selected genes and risk for prostate cancer


We have noted previously that individualized genetic tests sold directly to consumers and patients as tools to assess risk for prostate cancer (and other disorders) often don’t meet FDA guidelines for marketing in the USA. Now there are more questions about the value of such tests.

In a recent paper in BMC Medical Genomics, Carere et al. suggest that, although the use of such tests and provision of such “direct to consumer” genetic information does have “a measurable but modest effect” on the perception of cancer risk among individual patients, the degree of change in the individual’s perception of their risk as a consequence is often affected significantly by how the individual already perceives his or her level of risk and that the ability of the specific tests used in this study to change  behavior and induce changes to such activities as cancer testing/screening and prevention may be limited.  In other words, one may be spending a lot of money for information that has very limited actual value.

The “New” Prostate Cancer InfoLink wishes to be very clear that, based on the information available to date, we are extremely skeptical about the medical use of any of the available “direct to consumer” genetic information. It is one thing to be able to use such information to get some idea of whether your ancestors were largely from Scotland or Russia, or whether you carry a gene suggesting that you are one of (probably) millions of people descended from Ghenghis Khan  — a man known to have fathered very large numbers of offspring on many different women. It is quite another for us to be able to use such information with accuracy to predict risk for a diagnosis of cancer in a specific individual without careful medical guidance. The fact that (in our opinion) the data from this study support our level of skepticism could arguably be seen as bias in our reporting of the results.

Carere et al. surveyed customers of two different “direct to consumer” genetic tests at three different time points: before they received any results, and at 2 weeks and 6 months after delivery of the results. For each of four different cancers (breast, prostate, colorectal and lung cancer) they measured, “perceived risk” (PR) on the part of recipients — using a 5-point scale ranging from “much lower than average” to “much higher than average.” They also divided the customers’ genetic results into two groups: elevated risk and average risk.

Here is what they found:

  • 1,154 participants took the surveys.
  • There was an increase in perceived risk (+ve ΔPR) for lung cancer regardless of the actual test result.
  • +ve ΔPR values were significantly associated with elevated risk results for breast, prostate, and colorectal cancers.
  • −ve ΔPR values were significantly associated with average risk results for breast, prostate, and colorectal cancers.
  • In the case of prostate cancer specifically, at 2 weeks after receipt of the test results
    • ΔPR was +0.77 for patients exhibiting elevated genetic patients.
    • ΔPR was −0.21 for patients exhibiting average genetic risk.
  • Large and significant changes in ΔPR were evident only rarely
    •  < 4  percent of participants reported a ΔPR of ± 3 or more units (for all four cancer types).
  • ΔPR effects were apparently modified by a number of other factors, including age, family history of cancer, and baseline interest (for breast, colorectal, and lung cancer).
  • A pattern of decreasing impact on ΔPR over time was consistently observed (but was only significant only for colorectal cancer).

The table below shows data specific to risk for prostate cancer from this study (based on a total of 388 eligible survey responses). The percentages are the percentages of patients advised that they were at average or elevated risk for prostate cancer and how their perceived risk changed (ΔPR) compared to baseline at 2 and 6 weeks after receiving the test results.

PR

As one might expect, men told they were at elevated risk for prostate cancer based on the genetic test did indeed show an increase in their ΔPR compared to those told they were at average risk. What is perhaps more interesting is the numbers of men told they were at average risk whose perception of their risk increased at 2 weeks (43/278 or 15.4 percent) and 6 weeks (44/266 or 16.6 percent) or decreased at 2 weeks (25/76 or 33.0 percent) and 6 weeks (25/77 or 32.0 percent) post-baseline. Why would being told you were at average risk for prostate cancer either increase of decrease one’s prior perception to such a large extent? Equally, how could being told you were at elevated risk for prostate cancer actually lower one’s perception of personal risk for prostate cancer (which appears to have occurred in about 20 percent of men told they were at elevated risk)?

How truly significant is all of this? It’s hard to tell. But the truth is that for most genetic changes in most cancers we still really don’t know the degree to which any one or more genetic modifications are actually predictive of clinically meaningful cancer risk. By comparison, there are a few genes associated with some cancers that are highly predictive of cancer risk if they actually run in a family (but they may not be so predictive in a singular individual if the family history is limited or non-existent).

We still have an enormous amount to learn about the degree to which specific genetic characteristics are truly predictive for clinically significant prostate cancer. In the very humble opinion of The “New” Prostate Cancer InfoLink, we aren’t even close to being ready to use this type of testing to predict risk for prostate cancer unless one is testing for a specific gene because of a family history of the presence of that gene in a series of men, many of whom were diagnosed with progressive as opposed to just localized and potentially indolent forms of prostate cancer.

 

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