Survival and CTC data from the abiraterone acterate pivotal trial

As we have previously reported, the latest analysis of survival data from the pivotal Phase III trial of abiraterone acetate + predisone has shown a slight improvement in the survival benefit for patients treated with abiraterone (Zytiga™).

At a median follow-up of 20.2 months on treatment, patients with metastatic, castration-resistant prostate cancer (mCRPC) who had already progressed after at least one course of treatment with a docetaxel-based chemotherapy regimen did better when randomized to abiraterone + prednisone compared to the patients randomized to a placebo + prednisone.

When the original trial data were reported, the survival benefit favoring patients in the abiraterone + prednisone arm was 3.9 months. The new analysis shows the following:

  • Patients treated with abiraterone + prednisone showed a median survival of 15,8 months.
  • Patients treated with a placebo + prednisone showed a median survival of 11.2 months.
  • The median survival benefit favoring the abiraterone + prednisone arm of the trial had increased to 4.6 months (compared to the original 3.9 months).

In this presentation, Dr. Scher was also able to report that levels of circulating tumor cells (CTCs) in patients of the two arms of the trial correlated with patients survival. This means that, in the future, it may be possible to use levels of CTCs as a surrogate for overall patient survival. If the regulatory authorities in the USA and other countries are willing to accept this surrogate endpoint, it could make the conduct of trials of new drugs in late stage prostate cancer both quicker and less costly.

The Zytiga trial found that measuring CTC levels predicted a better prognosis and improved survival as early as 4 weeks after the initiation of treatment. However, this finding will need to be confirmed in other studies before a final determination can be made about the utility of CTC levels as a surrogate endpoint for overall survival..

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