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 biopharma company Regeneron (Nasdaq: REGN) slid as much as 13% in intraday trading today on heavy volume.

So what: Just yesterday Regeneron shares were soaring thanks to positive data from the company's Zaltrap drug. Today, they were giving some of those gains back as investors chewed on some data out of the National Eye Institute. The NEI found that Roche's drug Avastin worked just as well treating macular degeneration as the company's more expensive drug, Lucentis. Reuters reported that both Roche and Novartis (NYSE: NVS) -- Roche's partner on Lucentis -- generated $1.5 billion in Lucentis sales in 2010. At $50 per injection, Avastin is much cheaper than the $2,000 Lucentis.

Now what: While this has obvious implications for Roche and Novartis, Regeneron is currently working on its own macular-degeneration treatment -- VEGF Trap-Eye -- with Bayer. Should Avastin and its bargain price tag become an accepted treatment, it'd hardly be ideal for Regeneron. In the NEI study, there were more side effects reported from Avastin than Lucentis, but researchers said that the study wasn't large enough to confirm that the side effects were directly tied to Avastin. Regeneron shareholders will want to keep an eye on how this situation continues to develop.

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