ARN-509 posts Phase II data in CRPC and mCRPC at ESMO

There has clearly been a good deal of interest in the data on ARN-509 reported at the recent meeting of the European Society of Medical Oncology (ESMO) … at least from the investment community.

According to the media release issued by the company on October 1, the company presented data from an interim analysis of 93 patients. These 93 patients fell into three well-defined categories:

  • 25 men were metastatic and castration resistant (mCRPC) but had not received either abiraterone acetate or chemontherapy (the treatment-naive group).
  • 21 men were mCRPC, chemotherapy-naive, but had progressed after treatment with abiraterone acetate (the post-abiraterone group)
  • 47 men were non-metastatic, but were progressing on androgen deprivation therapy (ADT) (this is the nmCRPC group)

All 93 patienst appear to have been treated in open-label studies at a starting dose of 240 mg/day.

According to the company, among two the mCRPC patient groups:

  • After 12 weeks on treatment PSA declines of ≥ 50 percent from baseline were evident in
    • 88 percent of the men in the treatment-naive group
    • 29 percent of men in the post-abiraterone group
  • Median time to PSA progression
    • Had not been reached for the treatment-naive group
    • Was 16 weeks for men in the post-abiraterone group.
  • The objective response rate or ORR (as measured by RECIST criteria) was 63% in the treatment-naive group of men who had measurable metastatic disease at baseline.
  • ARN-509 was well tolerated in these 46 patients.

When we look at the data from the 47 men in the nmCRPC group, we find:

  • After 12 weeks on treatment,
    • PSA declines of ≥ 50 percent from baseline were evident in 91 percent of the men in the group.
  • After 24 weeks on treatment,
    • PSA declines of  ≥ 50 percent from baseline were still evident in91 percent of the men in the group.
    • 55 percent of patients had ≥ 90 percent decline in PSA.
  • The median time to PSA progression has not been reached.
  • ARN-509 was also well tolerated in these 47 patients.

While these data are certainly interesting and potentially promising, there has been no randomized trial of ARN-509 to date. Indeed, it is hand to quite know whether the regulatory agencies will allow AN-509 to be tested against a placebo in a randomized clinical trial any more (except in men who have failed all available options, which is clearly not going to be its “best” potential target audience). Aragon may be faced with difficult drug development questions in the not too distant future.

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