Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of AVEO Pharmaceuticals (NASDAQ:AVEO), a cancer therapeutics company, collapsed as much as 27% following the release of briefing documents today in anticipation of AVEO's meeting with the Food and Drug Administration panel on Thursday.

So what: If you recall, one of the oddities of AVEO's Tivozanib, an oral metastatic renal cell carcinoma drug, is that it outperformed Bayer and Onyx Pharmaceuticals' (UNKNOWN:ONXX.DL) Nexavar in terms of progression-free survival in trials (11.9 months versus 9.1 months), but actually delivered a slightly lower median overall survival than Nexavar (28.8 months versus 29.3 months). According to the briefing docs released this morning, it appears that the FDA may want AVEO to run an additional trial to confirm the added benefit of Tivozanib based on that reduction in overall median survival noted during the study.

However, AVEO CEO William Slichenmyer noted that when Nexavar-arm patients failed to respond or got sicker in trials, they were switched to Tivozanib, creating a sort of sequential instead of direct comparison late in the game. That could help explain the flip-flopped median overall survival figures.

Now what: Confused yet? We'll know more after AVEO meets with the FDA panel on Thursday. Safety doesn't seem to be a big issue here, but AVEO is going to need to convince the panel that another trial isn't needed if it has any hope of getting this drug to market within the next two years. Tivozanib clearly shows promise; but just how much promise remains to be seen.

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