New “liquid biopsy” tests of no known value in assessing risk of men for prostate cancer — yet


The “New” Prostate Cancer InfoLink  wishes to very clearly warn its readers about the near to complete lack of any meaningful data — as yet — supporting the use of a new form of test called a “liquid biopsy” in the diagnosis and monitoring of a range of different types of high-risk cancer (clinically significant, high-risk prostate cancer included).

Two commercial forms of liquid biopsy test were launched today by a San Diego, California-based company known as Pathway Genomics. The company’s media release refers to the two forms of the same test as the CancerIntercept™ Detect test — designed to detect tumor DNA in high-risk but otherwise healthy patients — and the CancerIntercept™ Monitor — designed to monitor patients with active or previously diagnosed cancer for risk of recurrence of their disease. The basic problem, however, is that the presence of DNA fragments of specific types circulating in a person’s blood stream is no guarantee at all that a particular patient is either at risk for clinically significant cancer of a particular type nor is it a guarantee of the recurrence of a former cancer. We are going to need a lot more information before we can establish such concepts with a high degree of accuracy.

A report on the Bloomberg web site today clearly states that:

While doctors are enthusiastic about the potential of liquid biopsies as a low-cost, non-invasive alternative to traditional tissue biopsies, they say more evidence is needed to validate the tests’ sensitivity before being offered to consumers, especially those without disease.

In the meantime, however, we suspect that many people with limited understanding of the basics of evidence-based medicine may be taken in by the marketing claims of Pathway Genomics. The “New” Prostate Cancer InfoLink strongly encourages all patients and their friends and family members to discuss these tests with your doctors before deciding to pay for them out of your own pockets. It is highly unlikely that any reputable cancer specialist or urologist is going to recommend the use of such tests until there is a good deal of data clearly showing an association between test results and the demonstrable presence of clinically significant cancer or recurrence of cancer post-treatment. What is more, no health care insurance company will be willing to reimburse for the use of such tests based on the available data.

The only definite consequence for patients from use of these tests at this time is that they will have paid several hundred dollars to be given data that has no real value in terms of clinical decision-making because it is not at all clear what the test results may (or may not) imply.

Having said that, we also want to be very clear that there is considerable future potential to the use of liquid biopsies in the diagnosis and management of several types of cancer … but only once there are sufficient data to allow us to understand the results of such liquid biopsies … and we are some considerable way from having such information today.

Pathway Genomics is clearly promoting these tests directly to consumers without any meaningful supportive data. It seems highly likely that the US Food and Drug Administration will be seeking ways to bar the company from  making public claims of the value of these tests until there are real data to support the effectiveness of the tests. Until the situation is clarified, we would suggest that patients paying for these tests out of their pockets are going to be sadly disappointed by the very limited value of the information made available to them.

4 Responses

  1. That is very confusing. I thought the FDA had to approve tests like that before any health claims could be made at all. There is a company called 23andMe that does partial genetic sequencing. (Founded by the former wife of one of the founders of Google). The company started offering a report that was based on published research tying various genetic variants to a propensity towards various diseases. The FDA swooped in a put a stop to that. 23andMe is now working with the FDA to try and get a pared down version of the report approved. Any supplement you buy that makes a claim such as “promotes heart health” includes a disclaimer that the claim is not FDA approved. The claims made by this test would seem more substantial than either of those.

  2. Doug:

    Independent laboratories that are CLIA certified do not necessarily have to get FDA approval to market the tests that they offer. For example, Bostwick Laboratories never had to get FDA approval to promote and market the Prostavysion test. But they market it primarily to urologists and oncologists, and they had data to back up the value of the test.

    There is, however, an issue related to exactly what you claim, as a marketer, that your test can do, and to whom you make such claims (even if you are CLIA certified). That was the reason that the FDA advised 23andMe to stop making the sorts of claims it was originally making for its genetic reports. The FDA is rarely happy about laboratories that promote tests like this directly to consumers and patients since the vast majority of consumers and patients simply don’t have the background knowledge necessary to understand what is being claimed.

    The degree to which the FDA is able to exercise controls over the promotion of dietary supplements (nominally foods as opposed to drugs) is a whole other issue.

  3. It is in agreement and the growing belief that “liquid biopsy” can provide a global longitudinal picture of tumor heterogeneity beyond tissue biopsy from the primary tumor. Especially, cell-free DNA (cfDNA) circulating in the bloodstream could soon become the unprecedented non-invasive, standard-of-care molecular marker for the treatment and management of cancer patients. However, the requirement of large sample volume, low yield, and labor-intensiveness are major obstacles for the routine application of cfDNA-based testing in the clinic. A proprietary cfDNA recovery/concentration method developed by CirculoGene enables clinicians to work with a sample volume as small as 20 ml (via a finger-prick), which can further expedite clinical decision-making and identify targeted therapies or experimental clinical trials for eligible patients in a time- and cost-efficient manner.

  4. Dear Ion:

    The theoretical potential of liquid biopsies is not an issue. What is an issue, on the other hand, to date, is proof of clinical value in medical decision-making for specific types of cancer … and most particularly for types of cancer (like prostate cancer) in which, as yet, we do not know precisely what types of information available from a liquid biopsy are determinants of high vs. low risk. Liquid biopsies will not give us Gleason scores, for example.

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