Week after week, several biotech stocks jump 30%, 40%, or even a lot more, thanks to positive clinical results, acquisitions, or other good news. Not this week, though. Few biotech stocks chalked up any positive gains in the wake of the market pullback.

Three biotech stocks still soared in spite of the general gloominess: ARMO BioSciences (NASDAQ:ARMO), Array Biopharma (NASDAQ:ARRY), and Karyopharm Therapeutics (NASDAQ:KPTI). Here's what caused these stocks to jump -- and whether or not any of them are good picks for investors now. 

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ARMO BioSciences

ARMO BioSciences stock zoomed close to 15% higher this week. And it did so without the company announcing any news. Not even a peep. With most stocks sinking over the last few days, how did ARMO seemingly defy gravity?

There's one important thing to know about the stock: It's brand new. ARMO BioSciences began trading on Jan. 26. The company itself isn't new, though. ARMO BioSciences was founded in 2010. It was originally named Targenics, but the biotech changed its name to ARMO BioSciences a couple of years later.

Some investors were eager to buy the stock. Unlike many biotechs that conducted an initial public offering (IPO), ARMO already has a pipeline candidate in late-stage development. The company is evaluating AM0010 in combination with a commonly used chemotherapy in treating pancreatic cancer, which has the worst mortality rate of all cancer types.

In an early-stage study, patients receiving a combo of AM0010 and FOLFOX -- a standard chemotherapy containing folinic acid, 5-fluorouracil and oxaliplatin -- experienced higher overall survival and one-year landmark survival rates than did patients taking FOLFOX alone. These results have some investors excited over the potential for AM0010 -- and for ARMO BioSciences.

Array Biopharma

Array Biopharma stock jumped more than 14% this week, which was a skyrocketing performance in comparison to the rest of the market. Unlike ARMO BioSciences and Karyopharm, though, Array actually reported some good news over the past five days.

On Tuesday, Array announced results for its fiscal 2018 second quarter. The biopharmaceutical company's top and bottom lines showed significant year-over-year improvement. But investors were more enthused about Array's clinical update.

The company's encorafenib-binimetinib combo achieved a median overall survival rate of 33.6 months in a late-stage study targeting treatment of BRAF-mutant melanoma. That was nearly double the 16.9 month median overall survival rate for patients in the study who received Zelboraf. Array had already reported results from this late-stage study, but the overall survival-rate improvement for its two-drug regimen generated plenty of excitement.

Array submitted a New Drug Application (NDA) for the combination of encorafenib and binimetinib to the Food and Drug Administration (FDA) last year. An approval decision is expected by June 30, 2018.

Karyopharm Therapeutics

Karyopharm Therapeutics stock moved 12% higher this week and was up more than 20% for the week on Thursday. As was the case with ARMO BioSciences, there wasn't any news over the last five days for Karyopharm. However, the stock still has some momentum from a big announcement made a couple of weeks ago.

On Jan. 25, Karyopharm announced that it had entered into an agreement for Biogen (NASDAQ:BIIB) to acquire experimental drug KPT-350 and other assets for the treatment of certain neurological and neurodegenerative conditions. With this deal, Biogen will pay $10 million upfront to Karyopharm. The small biotech is also eligible to receive milestone payments of up to $207 million.

The transaction leaves Karyopharm with four pipeline candidates in clinical development. Karyopharm's lead candidate is oral selinexor. The drug is being evaluated in two late-stage studies, one in combination with Velcade in treating multiple myeloma and the other in treating liposarcoma, a cancer that occurs in fat cells. 

Are they buys?

I'm intrigued by ARMO BioSciences and would love to see the biotech succeed with AM0010. However, my view is to wait on some late-stage results for the drug before taking any action with the stock. While the Biogen deal was good news for Karyopharm, I'm also in wait-and-see mode with this stock.

That leaves Array Biopharma. I think that chances for FDA approval for the encorafenib-binimetinib combo look pretty good. It's also great that Array has partnerships with several big drugmakers. The main drawback that I see for Array, though, is that high expectations are already largely baked into the stock price. Because of this, I'm hesitant to call Array stock a buy.

Keith Speights has no position in any of the stocks mentioned. The Motley Fool recommends Biogen. The Motley Fool has a disclosure policy.