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 cancer-drug researcher and longtime Rule Breakers recommendation Exelixis (Nasdaq: EXEL) are feeling good today, rising as high as 13.7% above Tuesday's closing price on more than four times average trading volumes.

So what: The company's fourth-quarter report showed lower revenues but also a smaller loss than expected. More importantly, and probably a bigger reason for the move, was the overview on prostate cancer drug cabozantinib that management provided in the earnings call.

Now what: In short, the cabo information is nothing but great news. Exelixis plans to start Food and Drug Administration testing of the drug for more than just prostate cancer later this year. If successful, those trials could open up vast new markets, and this is all the company is working on nowadays. Though fellow Fool Rich Smith disagrees, I wouldn't be surprised to see Exelixis swallowed up by a giant of the pharma field on the strength of cabo as a potential multimarket cancer-buster.

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Fool contributor Anders Bylund holds no position in any of the companies discussed here. Exelixis is a Motley Fool Rule Breakers selection. The Fool owns shares of Exelixis. 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 is investors writing for investors.