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June 9, 2009
Here's a fascinating (and alarming) look at the clinical data from the recent trial of Avastin (bevacizumab) in adjuvant colorectal cancer (that is, post-surgical therapy). This was an issue in the recent Roche/Genentech takeover, since it could significantly enlarge the market for the drug. According to the In Vivo Blog, the one-year interim look at the data (adding Avastin to the standard chemotherapy regimen) was nearly good enough to stop the trial early. There were 2,710 patients enrolled, and an additional six events would have pushed things over the top, statistically.
The trial went on, though, with two more years of standard therapy as follow-up. But by the (pre-set) three-year endpoint it turned out that there was no eventual real benefit to adding Avastin back in that first year. So what's the story? Is it that you need to keep giving the combination regime? Would those-one year results have held up? Or is this just a case of real long-term survival numbers wiping out what seems to be a promising short-term result?
It looks like Genentech may be gearing up to put that first theory to a test, and I wish them luck. Long-term tolerability will be an issue, and long-term cost will be a big one, too. They're going to have to show some pretty impressive numbers to overcome those two concerns. . .as impressive as, well, as those first-year interim ones they had. Will that effect dissipate or not?
Time and money will answer that little question. But for now, consider what would have happened if a few more patients had shown disease-free survival in time for that interim analysis. The trial would have been stopped early, all kinds of people would have gone on Avastin for their first year of adjuvant therapy. . .and this year we would have seen that it was apparently doing no good at all, at least in the take-it-for-a-year-and-stop mode. Clinical trial design: a real high-wire act.
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