What: Shares of Sarepta Therapeutics (NASDAQ:SRPT) rose by as much as 26% immediately after the opening bell today on the news that the FDA will need additional time to issue its final decision on the biotech's experimental Duchenne muscular dystrophy (DMD) drug, eteplirsen. The agency was scheduled to release its final verdict on the hotly contested drug by tomorrow.

So what: The market is apparently taking this delay as a sign that the FDA may greenlight the drug, despite the agency's serious doubts about its effectiveness.

Now what: Per Sarepta's press release, the FDA didn't earmark a new target review date. Rather, the agency only mentioned that it plans to complete the review in "as timely a manner as possible." Reading between the lines here, I think the FDA is likely very close to issuing a final decision, and perhaps only needed an extra couple of days to wrap up its review.

That said, I don't think this delay is necessarily a positive sign indicating that a conditional approval is forthcoming. After all, the FDA also extended its review of BioMarin Pharmaceutical's rival DMD drug, but ultimately rejected drisapersen's regulatory application. Moreover, the agency basically gutted eteplirsen's clinical program in its internal review, and the FDA's external panel of experts didn't exactly offer much in the way of a counterargument. In short, the most likely outcome remains a Complete Response Letter.   

As the FDA could surprise the Street either way, though, I'm perfectly content to watch this looming binary event from the safety of the sidelines.