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If you're looking for stocks that offer unusual growth opportunities, clinical-stage biotechs are fertile ground. Even among this select group, though, there are only a handful of companies that can realistically transform an initial investment of say $10,000 into a small fortune. 

The "trick," if you will, is to identify companies that are either developing, or have recently launched, franchise-level drugs that will allow them to build out a diverse product portfolio over time. The problem is that small companies with promising drugs -- experimental or otherwise -- tend to be bought out long before their full value is realized. What's left over are companies with drugs that tend to have substantial clinical or regulatory hurdles to clear, making them high-risk investing vehicles. 

For investors brave enough to continue down this rabbit hole, I think Acadia Pharmaceuticals (ACAD 1.78%)Amarin Corp. (AMRN 11.57%), and Sarepta Therapeutics (SRPT 2.82%)are all worth a deeper dive. Here's why. 

1. Acadia's flagship drug could be a megablockbuster

Last April, the FDA gave the green light for Acadia's Parkinson's disease psychosis drug Nuplazid, despite some serious concerns within the agency that it may increase the risk of death. The particularly intriguing part of the story is that Acadia priced its new drug at $23,400 for a year's supply, giving it the potential to generate upwards of $4 billion in peak sales within the U.S. alone. Total sales could rise markedly if Acadia is able to garner additional approvals overseas.

If that occurs, Nuplazid should easily provide enough free cash flows to greatly expand the biotech's clinical activities, and perhaps most importantly, enable it to make a splash on the M&A front. The obvious risk, though, is the ability of a young commercial operation like Acadia's to successfully handle a drug launch. After all, many companies simply decide to either sell themselves outright or sign a licensing agreement upon reaching this stage in their life cycle, admitting that bigger partners are better equipped to convince doctors to prescribe novel drugs such as Nuplazid. 

2. Sales of Amarin's fish oil pill are ramping up

After a tumultuous couple of years that saw Amarin take on the FDA over a number of issues regarding its highly refined fish oil pill Vascepa, the drugmaker's efforts finally appear to be paying off. Vascepa's sales are forecast to grow by nearly 70% this quarter compared to a year ago, and by roughly another 50% next year. Even so, Amarin's shares are presently trading at a mere 2.3 times the company's 2017 projected revenue. 

Amarin's shares are probably not garnering much of premium right now because of the pending interim data readout for Vascepa's large cardiovascular outcomes trial. It's scheduled for the third-quarter of this year, and it could prove to be a turning -- or breaking -- point in Amarin's story.

If this interim data analysis suggests that Vascepa does lower the risk of adverse cardiovascular events, the drug's sales should tick even higher than the present rosy forecast and put it solidly on the path toward becoming a blockbuster. Of course, a positive outcome is no guarantee, and a negative readout is equally likely, based on the body of published research on omega3 treatments so far. 

3. Sarepta is waiting for the FDA's final decision

Sarepta's story is tied to the regulatory fate of its Duchenne muscular dystrophy (DMD) drug eteplirsen. Given that there isn't a single drug approved to treat this deadly muscle-wasting disease at the moment, eteplirsen would almost certainly rake in hundreds of millions in annual sales if the FDA approves it. Perhaps even more importantly, though, a regulatory approval for eteplirsen would essentially validate the biotech's broader exon-skipping platform for DMD that could treat upwards of 80% of this diverse patient population.

While it's hard to estimate even a rough peak sales figure given that Sarepta's internal thoughts on pricing eteplirsen are still a mystery, industry experts have suggested that the company's DMD platform as a whole could easily generate over $1 billion in annual sales. Such a steady and sizable revenue stream would provide Sarepta with the firepower to pursue additional value-creating opportunities down the road. 

Last month, the FDA requested data from the company's ongoing confirmatory study of eteplirsen regarding the drug's ability to restore dystrophin production, implying that the agency would forgo a final approval decision until these data are considered. Although that development was definitely good news in light of the drug's negative advisory committee vote, Sarepta is arguably heading toward a make or break moment. If eteplirsen doesn't restore dystrophin levels to clinically meaninful levels, Sarepta's shares are going to have a tough time finding a bottom, as most of the company's value is tied to its DMD platform.  

Are any of these speculative biotechs worth the risk?

There's no doubt that a single misstep for any of these companies could cause its shares to tank in the blink of an eye. That's why I personally wouldn't add these stocks to my portfolio right now. Having said that, investors who are more comfortable with all-or-nothing type plays may want to consider these three names ahead of their upcoming clinical, commercial, or regulatory catalysts. After all, the market arguably hasn't built in much of a premium for any of these three -- meaning that they may be primed to skyrocket on positive news.