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 Halozyme Therapeutics (Nasdaq: HALO) rose 10% after a series of recent insider buys from board member Randall Kirk. The stock closed up 8%.

So what: Already owner of 7.5% of the biotech's outstanding shares, according to S&P Capital IQ, Kirk bought more than 277,000 shares last week. The biggest transaction -- for 166,100 shares -- came just before the Thanksgiving holiday.

Now what: Halozyme has been a huge winner since October, when the company and its distribution partner, Roche Holding, reported positive phase 3 trial results for breast cancer treatment Herceptin. Kirk apparently sees FDA approval as all but assured. Do you agree? Would you buy shares of Halozyme Therapeutics at current prices? Please weigh in using the comments box below.

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