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 biotech Ariad Pharmaceuticals (Nasdaq: ARIA) are plunging by as much as 13% today after a phase 2 study showed serious side effects from its experimental ponatinib drug.

So what: The American Society of Hematology released an abstract showing that 17% of chronic myeloid leukemia patients using the drug experienced serious side effects. As a result, roughly 15% of the patients stopped using the drug.

Now what: With as many studies, trials, and regulatory approvals any drug faces on the long and winding road to market, running up against any roadblock can have serious consequences. With only three drugs currently in the pipeline, the company has a lot riding on ponatinib. Last quarter's revenue totaled just $25.1 million yet the company commands nearly a $1.6 billion market cap; this stock deserves a little bit of bashing.

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Fool contributor Evan Niu holds no position in any company mentioned. Click here to see his holdings and a short bio. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.