What happened

Shares of Alnylam Pharmaceuticals, Inc. (NASDAQ:ALNY), a clinical stage biotech, gained 14.4% in June, according to data from S&P Global Market Intelligence. Investors were encouraged by a breakthrough-therapy designation announced at the end of May, increased investment from development partner Sanofi (NYSE:SNY), and the actions of a company insider.

So what 

Alnylam is one of the best-performing biotech stocks this year, and a breakthrough-therapy designation announced at the end of May helped push it a bit higher last month. Givosiran, the company's candidate for the treatment of acute hepatic porphyrias, significantly reduced occurrence of porphyria attacks among a small group of patients.

Excited investor in front of upward sloping stock chart.

Image source: Getty Images.

At the moment, there aren't any available treatments for the rare, life-threatening condition. The Food and Drug Administration (FDA) granted the experimental therapy a breakthrough designation, a program designed to expedite the regulatory process.

Crucial clinical-trial data regarding the company's most advanced candidate, patisiran, are expected any day now. If successful, it could become the first available therapy to prevent nerve damage caused by misfolded transthyretin. The condition is rare, but a successful launch could lead to peak annual sales of around $750 million.

French pharma giant Sanofi is developing patisiran in partnership with Alnylam and owns about 10% of the company's shares. Investors saw its purchase of an additional $21 million in Alnylam stock, and about $750,000 by the company's Chief Medical Officer, as hints of success in the soon-to-be unveiled data.

Now what

The breakthrough designation for givosiran gives the company increased access to Agency staff to help ensure that a larger late-stage clinical trial, slated to begin later this year, addresses the regulator's concerns. If the candidate can repeat results seen in the early-stage trial, odds of an approval seem strong. The nine patients evaluated in one of the study's treatment arms experienced a 63% reduction in annualized porphyria attacks.

While givosiran data and the breakthrough designation are encouraging, the highly anticipated patisiran results are going to either help this stock continue its run-up this year, or abruptly reverse its direction.

Cory Renauer has no position in any stocks mentioned. The Motley Fool owns shares of and recommends Alnylam Pharmaceuticals. The Motley Fool has a disclosure policy.