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 oncology company Ariad Pharmaceuticals, Inc. (NASDAQ:ARIA) plummeted 17% today after the U.S. Food and Drug Administration said that it's investigating its leukemia drug Iclusig.

So what: The stock plunged a whopping 66% on Wednesday after the FDA halted all new trials of Iclusig due to safety concerns, and today's announcement only raises more uncertainty among investors over the drug going forward. Specifically, the FDA is looking into the increasing number of reports of serious and life-threatening blood clots and severe narrowing of blood vessels in patients, prompting a few analysts to downgrade the stock on the risk of even more bad news ahead.

Now what: The FDA is urging doctors and patients to report side effects involving Iclusig.

 "Data from clinical trials and postmarket adverse event reports show that serious adverse events have occurred in patients treated with Iclusig, including heart attacks resulting in death, worsening coronary artery disease, stroke, narrowing of large arteries of the brain, severe narrowing of blood vessels in the extremities, and the need for urgent surgical procedures to restore blood flow," the FDA said in a statement. "The FDA is providing this information to patients and health care professionals while it continues its investigation. We are actively working to further evaluate these adverse events and will notify the public when more information is available."

So while biotech-savvy investors might want to take a deeper look at this issue and Ariad's assets, average Fools would probably do well to maintain their distance. 

Fool contributor Brian Pacampara has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. 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.