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What makes a cancer drug effective? What if it stops cancer from spreading when you give it to patients - is that effective, or not? This topic has come up around here before, but there may be a rather stark example of it unfolding with Aveo Pharmaceuticals (NASDAQ:AVEO) and its drug tivozanib.

Earlier this year, the company announced results of a trial in renal cell carcinoma of the drug versus the Bayer/Onyx drug Nexavar (sorafenib), which is the standard of care. It's not like Nexavar does a great job in that indication, though - when it was going through clinical trials, it ran in RCC patients versus placebo, since - you guessed it - placebo was the standard of care at the time. And while Nexavar did show a benefit under those conditions, there are still plenty of patients who don't respond. Thus tivozanib, and its window of opportunity. The compound itself is in the same broad chemical class (bi-aryl ureas) as sorafenib.

The Phase III results for the Aveo drug showed an improvement in progression-free survival - tracking the time it takes for the cancer to start spreading again. But progression-free survival does not necessarily mean "survival," not in the sense that cancer patients and their relatives really care about. Dying in the same amount of time, albeit with redistributed tumor tissue, is not the endpoint that people are waiting for.

The company is, of course, monitoring the patients that it's treated. And there's the problem: the current data show, after one year, that 77% of the tivozanib-treated patients are still alive. But 81% of the sorafenib patients have survived, and the FDA has officially expressed concern about the way things are going. That sent Aveo's stock down sharply the other day, as well it might. But there could be a way out:

Aveo said in today's statement that basically it's possible the preliminary survival data could be misleading. That's because in cancer trials like this one, cancer patients whose disease worsens on one drug can then go on to get a second drug which may help them. In this case, Aveo said 53 percent of the patients who were randomly assigned to get the Bayer/Onyx drug went on to get subsequent therapy after their disease worsened-and "nearly all" of them were given Aveo's tivozanib. By contrast, only 17 percent of the patients who were randomly assigned to initially get the Aveo drug went on to get a subsequent therapy. So it's possible that the patients in the Bayer/Onyx control group may be ending up living longer at least partly because of the Aveo drug they got later on.

We'll have to wait for more data to sort all this out. Until that point, Aveo (and its shareholders) are probably in for a bumpy ride. But it's worth remembering that renal cell carcinoma patients are having a rather harder time of it than anyone else in this story, and they're the people who will be watching this most closely of all. . .

Source: Does AVEO Pharmaceuticals' Tivozanib Work, Or Not?