Image source: PTC Therapeutics.

What: After the company reported second-quarter financials and said it hasn't given up on winning U.S. approval of Translarna, its therapy for Duchenne muscular dystrophy (DMD), shares in PTC Therapeutics (NASDAQ:PTCT) soared 27.1% today.

So What: PTC Therapeutics' Translarna won conditional approval for use in the EU in 2014; however, the FDA opted against reviewing the drug for approval in the U.S. last year. While the company is still awaiting word from EU regulators to see whether Translarna's conditional approval will be extended for another year, sales in the region have continued to grow. In the second quarter, Translarna sales were $15.4 million, up 150% versus a year ago.

In addition to delivering robust growth in Translarna sales, management also reported that it has appealed the FDA's decision not to review Translarna for approval in the United States. There's no guarantee that this appeal will result in a review of the drug; however, there's been considerable pressure on the agency to usher new DMD drugs to market.

Most notably, after a key FDA advisory committee voted against early approval of Sarepta Therapeutics DMD drug eteplirsen in April, the agency delayed making its final go/no-go decision indefinitely amid a groundswell of support from patients and advocates.

Now What: PTC Therapeutics appears hopeful that it can ride the coattails of patient advocacy to win consideration for Translarna, but investors should probably focus more in the near term on the ongoing discussions the company is having with EU regulators.

Conditional approval of Translarna requires annual review and renewal of approval. While that re-approval had been scheduled for mid-year, EU regulators have informed management that they'll require more time to make their decision. To secure support, PTC Therapeutics plans to share a draft clinical trial protocol with decision makers soon. 

Assuming that Translarna remains on the market in Europe, the pace of Translarna's sales put the drug on target to deliver on PTC Therapeutics' goal for at least $65 million in sales this year. The company also hopes to have data in hand that could support a label expansion for Translarna to include cystic fibrosis patients with an amenable genetic makeup.

Overall, PTC Therapeutics' question marks should give most investors reason for caution. However, if some of its questions get resolved in the coming months, it might be worth another look.

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.