CTC count as a biomarker for response to chemotherapy in men with mCRPC

There is increasing evidence that circulating tumor cell (CTC) count may be important in assessing the likelihood for an optimal response to treatment with docetaxel-based chemotherapy for men with metastatic, castration-resistant prostate cancer (mCRPC).

Okegawa et al. have just reported new data on this topic from a series of 57 Japanese men with mCRPC, all of whom had failed standard forms of androgen deprivation therapy (ADT) and were then given docetaxel-based chemotherapy. However, it seems unlikely that any of these men had received either abiraterone acetate or enzalutamide prior to chemotherapy.

Here are the core study findings:

  • The median CTC count for all 57 patients prior to initiation of chemotherapy was 7 CTCs per 7.5 ml of blood; however …
  • The range for the CTC count was very high (from 0 to 227 CTCs per 7.5 ml of blood).
  • 24/57 patients (42.1 percent) had a CTC level of < 5 CTCs per 7.5 ml of blood.
  • 27/57 patients (47.4 percent) had a CTC level between 5 and 50 CTCs per 7.5 ml of blood.
  • 6/57 patients (10.5 percent) had a CTC level > 50 CTCs per 7.5 ml of blood.
  • Patient survival ranged from 6 to 37 months from initiation of chemotherapy.
    • Median survival was 15.3 months.
    • Mean survival was 12.8 ± 8.1 months.
  • When the authors compared the survival of patients grouped on the basis of the CTC level at initiation of chemotherapy,
    • The 24 patients with a CTC count of < 5 had a median overall survival of 25.0 months.
    • The 33 patients with a CTC count of ≥ 5 had a median overall survival of 10.5 months.
    • This difference was statistically significant (p < 0.001).
  • CTC count and alkaline phosphatase level were each found to be independent predictors of overall survival time.
  • Poorer overall survival was also predicted by a CTC count of ≥ 5 after three courses of docetaxel-based chemotherapy.

Okegawa et al. conclude that:

The CTC count may be an independent predictor of overall survival in patients with mCRPC treated with docetaxel chemotherapy. The numbers of CTCs detected was important in assessing response to chemotherapy and predict disease outcome.

What is less clear at this time is whether CTC count is really a significantly better predictor of overall survival for men with mCRPC than the patient’s alkaline phosphatase level.

5 Responses

  1. This paper by medical oncologist Howard Sher of MSKCC provides a much better accounting of the value of CTC testing.

  2. Dear Chuck:

    Dr. Scher’s article is certainly more complete … but what happens in places like MSKCC is not exactly representative of widespread clinical practice, and what Dr. Scher says in his article still doesn’t offer us compelling evidence that monitoring CTC count is any better than monitoring alkaline phosphatase as an indicator of prognosis (let alone potential as a surrogate marker for survival).

    And we should be very clear that most oncologists are not (as far as I am aware) currently using CTC counts as a way to monitor men with late stage prostate cancer. The reason for that probably has more to do with Dr. Scher’s comments at the end of his article … the ones about what’s really important to the patient!

    The article above does at least seem to provide us with independent confirmation that a CTC count of < 5 may define a cut-point for longer-term survival than a CTC count of 5 and higher.

  3. What I am curious is how they picked 5 as the number? The range was 0-227. The sample size is not large: 27 patients had CTCs were = or > 5. I wonder what the range is. My CTCs have always been low. Last test was 11.

  4. Dominic:

    Researchers like Howard Scher and his colleagues at Memorial Sloan-Kettering have long believed that a CTC count > 5 is associated with greater risk for earlier disease progression (see the link provided by Chuck Maack above).

  5. Thanks . I’ll try to find the journal articles referenced in Scher’s article to see how they established 5 as the cutoff.

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