Santa came early for some investors. Several health-care stocks took a sleigh ride up the charts. Here are three of the most humongous performers over the past week.

Giddy from Gilead
If you owned shares in YM Biosciences (NYSEMKT: YMI), you're undoubtedly giddy right now. Gilead Sciences (GILD -0.84%) announced a buyout of the small company for $510 million. YM Biosciences shares shot up nearly 78% for the week on the news.

With the deal, Gilead picks up YM's JAK inhibitor CYT387. The drug showed solid results in a phase 1/2 study targeting treatment of myelofibrosis. Gilead plans to launch a phase 3 trial in 2013 following completion of the acquisition.

Gilead already has its own drug, GS6624, in a phase 2 study for treating myelofibrosis. Unlike YM's CYT387, GS6624 works by attaching to cancer cells and marking them in a way that makes it easier for the body's immune system to attack the cancer. With two drugs taking different approaches, Gilead could emerge at some point as the leader in the myelofibrosis market.

Up early
Infinity Pharmaceuticals (INFI) shares skyrocketed nearly 39% this week. The company announced more data from its ongoing phase 1 study of  IPI-145 in treating patients with advanced blood diseases.

You might want to read that last sentence one more time. Shares were up by a whopping amount on data from an early stage study that is still under way. Yep, that data definitely sounded good to investors. Patients responded well to IPI-145 across several types of blood disorders and those positive results were obtained quickly. 

Understandably, Infinity's management were thrilled. Analysts enthusiastically joined into the fun with upgrades of the stock. Stifel Nicolaus recommended the stock as a buy and raised its target price for Infinity to $30 per share. RBC bumped its target price from $28 per share to $32 per share. Infinity opened the week below $22 per share. 

Synta Claus
Synta Pharmaceuticals (NASDAQ: SNTA) delivered a nice present to its shareholders this week also. Shares jumped nearly 16% for the week.

Two developments likely contributed to Synta's rise. On Tuesday, an online article noting several upcoming catalysts for the company was published. The next day, Synta announced a direct stock offering where several members of its board of directors and institutional investors planned to buy 7 million shares. That kind of insider buying inspires confidence.

It won't be surprising to see considerable fluctuation in Synta's stock over the coming months. However,  good results from phase 3 trials of ganetespib could land Synta on the humongous list again in the future.

Jolly
Increases of 16% to 78% in one week tend to make investors quite jolly. However, the world of health care is quite volatile. Today's jolliness can quickly morph into tomorrow's gloom. I don't think that will be the case with our humongous performers from this week, but you never know if a stock will drop as quickly as a fat man down a chimney.