Source: Flickr user Bill Brooks

In the fast-paced world of biotechnology, news can happen fast, and when it does, it can result in eye-popping moves. For instance, here are three under-the-radar biotech stocks soaring higher by nearly 100%, or more, over the past 13 weeks. Read on to learn what has got investors so excited about these companies and whether or not you might want to consider them for your portfolio.

No. 1: Retrophin Inc (NASDAQ:RTRX)Retrophin shares have sky-rocketed by over 100% in the past few months on optimism that its rare-disease focus and aggressive pricing schemes can turn it into a leader in orphan drugs.

So far, the company markets three drugs: Thiola, Cholbam, and Chenodal, but two of the three are new to Retrophin.

Thiola is a long-standing therapy for an ultra-rare condition in which patients continuously suffer from kidney stones. Retrophin acquired the rights to Thiola last year and as a part of a relaunch, hiked the price significantly. That strategy should sound familiar given that a similar scheme turned Mallinckrodt's Acthar Gel from all-but-forgotten drug into a therapy with $228 million in sales during Q1.

Cholbam is the other new addition to Retrophin's line-up. The FDA approved Cholbam in the first quarter and, following its approval, Retrophin exercised a very attractive provision that allowed it to acquire all the rights to the drug from Asklepion Pharmaceuticals, LLC -- a privately-held company -- in exchange for $27 million upfront, 661,278 shares, $37 million in potential milestones, and tiered royalties. In addition to landing Cholbam, the first therapy for the treatment of children and adults with bile acid disorders caused by single enzyme defects, the deal also landed Retrophin with an FDA pediatric priority review voucher that Retrophin just sold to Sanofi for $245 million.

Assuming that Retrophin's decision to boost Thiola's sales force and launch Cholbam pay off, then Retrophin could find that its product sales head nicely higher than the $17.4 million recorded in the first quarter. If so, then Retrophin could be worth more than its $1 billion market cap; but only time will tell, so buyer-beware.

No. 2: Eagle Pharmaceuticals Inc. (NASDAQ:EGRX)Eagle Pharmaceuticals is starting to see the benefits of its strategy of reformulating existing therapies to make them safer and easier to use.

Last fall, Eagle Pharmaceuticals rolled out a less-concentrated version of dantrolene called Ryanodex that can be administered more quickly, and sales of the drug are beginning to gain traction. In the first quarter, Ryanodex revenue totaled $1.6 million, up 200% quarter over quarter, and unaudited sales in April reached $600,000.

Since hospitals are required to stock dantrolene, which is used to treat malignant hypothermia MH -- a condition caused in some patients by contact with inhaled anesthetics or specific muscle relaxants used in surgery -- sales could continue to grow as more institutions switch over to its improved formulation.

Investors are also applauding the company's recent agreement to license its bendamustine rapid infusion product to Teva Pharmaceutical (NYSE:TEVA).

Teva Pharmaceutical paid Eagle $30 million upfront and agreed to pay up to another $90 million in milestones, as well as double-digit royalties for rights to Eagle Pharmaceuticals' bendamustine product. By licensing this drug from Eagle Pharmaceuticals, Teva Pharmaceutical is protecting market share for its own bendamustine HCI drug, Treanda, which had sales of $767 million last year.

Eagle Pharmaceuticals could also add another product to its bench if the FDA approves its ready-to-use bivalirudin formulation of The Medicines Company's $600 million per year Angiomax. Eagle Pharmaceuticals filed for FDA approval of that product on May 20.

It's not clear to me how much Ryanodex' sales could peak out at, or how much of Treanda's sales Eagle Pharmaceuticals' bendamustine will capture, but these drugs, plus the potential sales tied to other drugs in development, make this stock interesting.

No. 3: bluebird bio (NASDAQ:BLUE)Bluebird bio has also delivered nearly triple-digit returns for investors over the past few months as the company's market cap sky-rocketed to $6.4 billion.

That's a pretty lofty valuation for a clinical-stage company that doesn't have any products on the market, and for that reason investors will need bluebird bio's pipeline to produce some blockbuster therapies.

The closest of bluebird bio's drugs to market is Lentiglobin BB305, a gene therapy for use in treating beta thalassemia major patients. BB305 is an infusion drug therapy that involves inserting a functioning beta globin gene into a patient's own hematopoietic stem cells outside the body and then infusing those cells back into the body. The therapy has shown promise in clinical studies, and meetings with FDA and EU regulators have bluebird bio encouraged that it could soon file for EU approval, with an FDA filing coming later.

Bluebird bio's pipeline also includes Lenti-D for childhood cerebral ALD and pre-clinical blood cancer therapies that are being developed with Celgene. Bluebird bio has also entered into a collaboration deal to work on CAR-T therapies that help a patient's immune system better identify and destroy cancer cells.

All of these programs are intriguing, and some of them take on rare diseases that are likely to command premium pricing, but there's a lot of risk in this one to investors -- especially given its current valuation. For that reason, chasing this stock higher might not be the best bet.

Tying it together
Investors should be cautious about rushing into stocks simply because they've been top performers, and since all three of these biotech stocks have made significant moves, a pullback could be coming. If so, then investors will be best served by watching these three companies to see if they come down to prices that may make them more attractive. Regardless, I think that only highly risk-tolerant investors should consider investing in these companies.