The prognostic value of CTCs in low-volume prostate cancer

Circulating tumor cell (CTC) levels have clearly been shown to have relevance to the prognosis of men with metastatic, castration-resistant prostate cancer, but we still know little about their potential importance in men with early stage disease.

Ali et al. have attempted to assess the incidence of circulating tumor cells (CTCs) after radical prostatectomy (RP) in a cohort of prostate cancer patients with low-volume tumors (< 0.5 cm3).

After radical prostatectomy, they took blood samples from 64 patients to assess their CTC levels. Only 9/64 patient actually met criteria for low-volume prostate cancer, and among these 9 patients:

  • 7 had detectable levels of CTCs.
  • PSA elevation was evident in 2/7 patients with detectable CTCs.
  • The detection of CTCs did not predict biochemical failure.

It is possible that if one tested such men for CTC levels regularly over time, one could correlate rising CTC levels with rising PSA levels, but this would likely not add a great deal to our ability to project risk for men who were already at evident risk from biochemical failure.

Many men showing CTCs in blood soon after radical prostatectomy may be sufficiently immunologically competent to eliminate such cells naturally within a relatively brief period of time after surgery. This does raise the question whether men with early stage disease and suppressed immune systems are at any greater risk from CTCs immediately post surgery.

11 Responses

  1. Since you didn’t mention it, I’m guessing there must be some reason that CTCs don’t have a diagnostic value for prostate cancer. Why is that?

  2. Well CTCs probably do have a potential diagnostic value in men who are initially diagnosed with very advanced forms of prostate cancer, but it probably wouldn’t be a very useful value by comparison with a bone scan and a PSA test.

    CTC tests are expensive to run, and as far as I know, no one has ever demonstrated that a specific CTC level was definitively associated with a diagnosis of prostate cancer in men with localized disease. I have also never heard anyone suggest that running a CTC test in men suspected with localized, untreated prostate cancer would be a good idea, but I can’t tell you exactly why.

    You might want to look at this presentation from the ASCO meeting in 2009. (It includes a lot of uses of the word “may”.) See also this Medscape article from AACR this year. Clearly the manufacturer is interested in use of the CTC chip technology to monitor disease progression, but whether this is truly clinically valuable (by comparison with PSA data) doesn’t seem to be evident yet.

    As far as I am aware, the only really widely accepted use of the CTC test to date is in the monitoring of patients with late stage disease in clinical trials. As yet I don’t think even the average patient with mCRPC has his CTCs measured on a regular basis.

  3. So according to that study every patient has CTCs after surgery and then they disappear in some. Does that not already mean the cancer is sytematic and how do we know one of these cells don’t just lodge someplace in the body? Wouldn’t that explain the reccurence in some patients who were supposedly organ confined.

  4. No, it does not mean the cancer is systemic. For the cancer to be systemic it must be growing outside the prostate, not merely present at a point in time. Clearly the presence of CTCs doesn’t allow one to define who recurrence is going to occur in (any more than the RT-PCR test did 15 years ago). The presence of CTCs is not a definitive indicator of metastasis, although it may be an indicator for risk, but then so is a risking PSA.

  5. I had RP two years ago. If I went and had this test and no cells were found then I would probably be at an even lower risk for recurrence? It I had CTC present I most probably will recur.

  6. Sorry that was sort of a question. Will anyone perform thus test if I ask? I think it would be logical if you have CTCs this long after surgery you will likely reccur.

  7. Chris: I am sure someone would be willing to give you the test if you want to pay for it. (I don’t think your insurance company will.) However, I am yet to be convinced that a low CTC level in someone like you is necessarily a signal of prostate cancer recurrence if you have an undetectable PSA.

  8. But, if I am cured there should be none at all. Correct?

    My PSA test 2 weeks ago was <0.03. I would think that if you are positive for prostate cancer-specific CTCs, then your cancer has already escaped your prostate. Maybe I don't understand this concept, but it would seem logical to me that you have systematic desease if you are positive for CTCs. Maybe they haven't formed a metastatic tumor yet, but I would think that they will. If your immune system could not recignize and kill the cancer cells in your prostate, why would it be able to clean them out of your blood?

  9. Your argument is theoretically viable. But that doesn’t mean I (or perhaps anyone else) can give you clinically accurate and meaningful answers. The only accurate answer that I can give you is, “I don’t know.”

    The thing that I “don’t know” with absolute certainty is that if you have a CTC count of zero at a specific point in time that you will never have a recurrence. All that I can really tell from a CTC count of zero is that your CTC count was zero at that point in time!

  10. Great, I stumped the sitemaster. I guess I was alarmed that 7/9 people were positive

  11. Am I the only one who sees a 300 lb gorillia in the room on this one?

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