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What: Shares of Sarepta Therapeutics (NASDAQ:SRPT) surged by more than 36% immediately after the opening bell on Tuesday as a result of the FDA requesting dystrophin data from the company's ongoing confirmatory study of eteplirsen. Eteplirsen is an experimental Duchenne muscular dystrophy (DMD) drug that's currently under regulatory review by the FDA. 

So what: This data request implies that the agency may be willing to grant the drug accelerated approval -- that is, if the company can show that eteplirsen does increase dystrophin levels as advertised. As a reminder, the agency and the company were clearly at odds over this critical point during the drug's recent advisory committee meeting. 

Now what: Although Sarepta said that it will submit the biopsy samples in the coming weeks, there doesn't seem to be a firm deadline in place regarding the drug's final decision. So, it's looking like investors and patients will have to wait yet another two to three months for the final word from the FDA. 

On the bright side, this intriguing data request does offer some hope that eteplirsen could eke out an accelerated approval, despite the overwhelmingly negative internal review from the FDA and its panel of outside experts. The bottom line is that if eteplirsen does restore dystrophin expression in a clinically meaningful way, then it should be approved. And the FDA knows that.

The FDA is concerned about rejecting a drug for a fatal disorder that actually works. The agency, after all, would effectively be denying patients a life-saving therapy. At the same time, there must be clear evidence of a drug's efficacy to merit approval, and the fact of the matter is that Sarepta has, as of yet, failed to meet this requirement.

While I'd be delighted to see that this drug works, investors need to bear in mind the dire consequences for Sarepta's stock if these biopsies fail to satisfy the FDA's concerns. After all, eteplirsen's efficacy is essentially on the line here, perhaps along with the fate of Sarepta's entire exon-skipping DMD platform. So even though eteplirsen's chances of approval are arguably better today than they were yesterday, Sarepta's steep risk profile hasn't changed as a result. That's why I'm comfortable watching this speculative biotech from the safety of the sidelines.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.