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June 23, 2009
Medarex, Ipilimumab, Prostate Cancer, And Reality
What's really going on with Medarex and ipilimumab? The company made news over the weekend with a press release from the Mayo Clinic, detailed what appears to be a substantial response in two prostate cancer patients. But the more you look at the story, the harder it is to figure out anything useful.
As this WebMD piece makes clear, this study is not a trial of ipilimumab as a single agent. The patients are undergoing prolonged androgen ablation, the testosterone-suppressing therapy that's been around for many years and is one of the standard options for prostate cancer. The trial is to see if ipilimumab has any benefit when it's added to this protocol - basically, to see if it can advance the standard of care a bit.
WebMD quotes Derek Raghavan at the Cleveland Clinic as saying that androgen ablation can sometimes have dramatic results in patients with locally advanced prostate cancer, so it's impossible to say if ipilimumab is helping or not. That's why we run clinical trials, you know, to see if there's a real effect across a meaningful number of patients. But (as this AP story notes) we don't know how many patients are in this particular study, what its endpoints are, or really anything about its design. All we know is that two patients opted out of it for surgery instead. (Credit goes to the AP's Linda Johnson for laying all this out).
Ipilimumab is an antibody against CTLA-4, which is an inhibitory regulator of lymphocytes. Blocking it should, in theory, turn these cells loose to engage tumor cells more robustly. (It also turns them loose to engage normal tissue more robustly, too - most of the side effects seem to be autoimmune responses like colitis, which can be very severe. The antibody has been studied most thoroughly in melanoma, where it does seem to be of value, although the side effect profile is certainly complicating things.
So overall, I think it's way too early to conclude that Medarex has hit on some miracle prostate cure. This press release, in fact, hasn't been too helpful at all, and the Mayo people really should know better.
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