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 Human Genome Sciences (Nasdaq: HGSI) soared a staggering 100% after drug giant GlaxoSmithKline (NYSE: GSK) offered to acquire it for about $2.6 billion.

So what: Glaxo's offer values Human Genome at $13 per share and represents a whopping 81% premium to its Wednesday closing price. However, Human Genome's board rejected the offer as inadequate, fueling investor hopes of an even higher bid.

Now what: Human Genome said it has hired Goldman Sachs and Credit Suisse to help with the exploration of alternative strategies, which includes a possible sale of the company. Of course, the purchase of Human Genome would give Glaxo full rights to their partnered drugs and generate a whopping $200 million in cost synergies within a couple of years, so there's a good chance that Glaxo will indeed pay up to get the deal done. For lucky Human Genome shareholders waking up to today's whopping 100% gain, though, taking at least some dough off the table still seems prudent.

Interested in more info on Human Genome? Add it to your watchlist.