Last month, shares in most biotech companies moved higher as investors began returning to the basket following a significant drop in the first quarter. Among those leading the move higher were MannKind (NASDAQ:56400P706), Intrexon Corp (NASDAQ:XON), and Ophthotech Corp (NASDAQ:OPHT).

Since few industries are as hit-and-miss as biotechnology, where stocks move on whims and whispers tied to even the flimsiest trial data, the industry is best suited for only the heartiest of investors. With that in mind, let's take a closer look at the catalysts driving shares in these three higher this past month.

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1. MannKind
Excitement surrounding MannKind is tied to Afrezza, a treatment for type 1 and type 2 diabetes that is under consideration for approval by the FDA after previously being rejected twice.

Mannkind recently got a positive recommendation for approval from a key FDA advisory panel, helping clear the way for a potential go-ahead when the FDA makes its final decision by July 15.

If approved, bulls think MannKind could be set for a revenue windfall over the coming years as diabetics supplement their current injectable insulin with the inhalable Afrezza. 

According to Express Scripts, Americans already pay more for diabetes treatment than for any other condition and that spending is set to jump as the number of people diagnosed with diabetes climbs from 365 million people to 550 million people by 2030.

That may offer plenty of sales tailwinds, but Afrezza hasn't been approved (yet) and there's no guarantee that if it is approved it will live up to sky-high projections. Certainly, a well-heeled partner with an existing diabetes sales and marketing team could come team up with MannKind for a successful launch, but there's no guarantee of that happening either. Regardless, buyers and sellers (29% of the shares available for trading are held short) will have to wait and see if Afrezza gets approved in July.

2. Intrexon Corp
Intrexon is working on a slate of projects in a bid to prove that altering DNA can have positive, profit-friendly implications across a variety of industries.

The company is developing gene-enhanced salmon that grows more quickly than wild salmon, working on a biofuels program that could conceivably help natural gas replace crude oil, and it's (of course) collaborating to discover new gene-based therapeutics to treat disease.

If all this sounds too good to be true then you'll likely agree with me that this company is about as speculative as you can find.

Intrexon's shares have rallied from less than $14 in early May to more than $23, yet the company has virtually no revenue (just $4 million in the first quarter) and big losses (more than $36 million in Q1). To me, that's an investment that's too far out in front of its skis.

3. Ophthotech
Ophthotech's shares soared by more than 20% in one day last month following news Novartis (NYSE:NVS) is teaming up with it on its promising eyesight drug Fovista.

In order to lock-up international sales of Fovista, Novartis inked a big-time deal with Ophthotech that includes $200 million up front. That deal shores up sales of Novartis' blockbuster Lucentis, which despite facing competition from Regeneron's Eylea still generated more than $620 million in ex-U.S. sales for Novartis' in the first quarter.

Ophthotech is already conducting phase 3 studies of Fovista used alongside Lucentis for wet-AMD, and the company plans a similar phase 3 study for Fovista used alongside Eylea. In early stage trials, patients receiving Fovista saw an improvement of 10.6 letters of vision at 24 weeks, compared to 6.5 letters for patients receiving Lucentis alone.

If Fovista can continue to put up those type of results in phase 3, Ophthotech could end up getting as much as $1 billion in payments from Novartis, including milestones. Ophthotech also stands to receive royalties on ex-U.S. sales if Fovista is approved overseas. Investors will need to wait a while, however, to see if that happens since results from the phase 3 trials won't be available until 2016.

Fool-worthy final thoughts
MannKind investors will be watching closely to see whether the FDA is willing to give Afrezza the green-light in July. If it does, shares could go considerably higher given the substantial short interest, but if it doesn't MannKind's weak cash position could make for some difficulties moving forward.

Meanwhile, Intrexon is an intriguing company, but it's yet to turn its promise into profit. Given the significant jump in its shares last month, most Fools should simply look elsewhere, such as to Ophthotech.

Ophthotech may still be years away from having data to present to regulators, but Fovista targets a multibillion dollar revenue indication and Ophthotech's deal with Novartis' means there's plenty of milestone revenue potential. Additionally, since Ophthotech's C-suite is led by David Guyer, the former founder of Eyetech, it wouldn't be surprising to see a suitor in the company's future. OSI Pharmaceuticals bought Eyetech back in 2005 for nearly $1 billion in order to get its hands on Macugen, an early Lucentis competitor.