Use of CTCs to assess response to abiraterone acetate at 12 weeks on therapy

Back in 2011 we reported a presentation by Scher et al. indicating that circulating tumor cell counts (CTCs) could probably be used to monitor responses to abiraterone acetate (and perhaps other forms of drug therapy) in the treatment of men with metastatic, castration-resistant prostate cancer.

The published report of this finding has only now been published in the Journal of Clinical Oncology, and we have to say that we find it somewhat distressing that it has taken nearly 4 years from the time this finding was first reported until actual publication of the peer-reviewed paper. We should note that in the final report, the authors actually indicate that the combination of CTCs and levels of lactate dehydrogenase (LDH) satisfy all four of the so-called “Prentice criteria” for an individual-level surrogate endpoint.

It appeared to be clear from the original report — and it is certainly clear from the finally published article — that assessment of CTCs (along with LDH lavels) at 12 weeks on therapy with abiraterone acetate can be used to evaluate the likelihood of patient response at just 12 weeks on therapy. The relevant information is also summarized in detail in a commentary on the ScienceDaily web site.

Quoted on the ScienceDaily web site, Dr. Johann de Bono, one of the study leaders, states that:

Our study showed that circulating tumor cells act as an early warning test for men who are not responding to treatment — potentially allowing doctors to switch patients early to alternative options. We hope our results will not only lead to better use of the current range of treatments, but also speed up the discovery of new drugs by providing an important new tool to the researchers trialling them.

The “New” Prostate Cancer InfoLink would have similar hopes, particularly with relation to the use of these tests to prevent the unnecessary over use of abiraterone acetate in patients who are clearly not responding to this very expensive forms of treatment.

3 Responses

  1. Excellent and very useful information.

    Please keep up your terrific reporting.

  2. How readily available is the CTC test and at what cost? Chuck Maack reports it can be obtained at Quest, although I have no idea of cost.

    A couple of men I know who have requested the test at institutions of excellence in the past 6 months have been told it is not available — although I know Johns Hopkins, MSKCC, and a maybe a couple of others can perform CTC measurements.

    The 12-week cut-off seems long at this point in history. For example, in the 1K/2K abiraterone trial at UCSF last year, men who did not respond based on PSA levels within 30 days were eliminated — with no CTC testing … and that is a cheap and accessible marker.

  3. Rick:

    The CellSearch CTC test is a commercially available test that any physician or hospital can choose to use or not use. Whether they do actually choose to use or not use it is likely to depend on perspectives about the real value of the test in the majority of patients. There is a big difference between the value of a test like this in clinical trials as a potential (but as yet unestablished) surrogate endpoint for survival (which could be considerable if it is sufficiently accurate), and the value of the test in actual monitoring of an individual patient, which is a great deal less clear.

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