What happened

As of 1:18 p.m. EDT on Thursday, shares of Alnylam Pharmaceuticals, Inc. (NASDAQ:ALNY) are up 13.7%, while shares of its biotech peer Ionis Pharmaceuticals Inc. (NASDAQ:IONS) are down 8.1%.

Investors are cheering positive results from the late-stage Apollo trial with Alnylam's lead candidate, patisiran. The top-line data suggest patisiran could have a competitive edge over a candidate being developed by Ionis.

So what

Alnylam's rally today probably would have been more dramatic if it hadn't already told everyone the Apollo trial met its primary endpoint over a month ago. Today's announcement included more details that don't bode well for Ionis and its related candidate, inotersen.

Collage of rising figures in green and falling figures in red

Image source: Getty Images.

In partnership with Sanofi (NYSE:SNY), Alnylam is developing patisiran for the treatment of nerve damage caused by a buildup of misfolded transthyretin. After 18 months of treatment, patients given patisiran exhibited a 34-point benefit on the mNIS+7 scale, a generally accepted scale of disease activity, compared to those receiving a placebo.

Patisiran wasn't evaluated in a head-to-head study with Ionis' candidate, but a comparison of available data might explain why Ionis' former partner GlaxoSmithKline handed back all rights to inotersen a few months ago. Even if Ionis eventually launches inotersen, its 19.7-point benefit over placebo, observed on the mNIS+7 scale at 15 months, strongly favors Alnylam's drug.

Now what

Patisiran is the most advanced of several programs in Alnylam's clinical-stage development pipeline, and investors can look forward to a flurry of activity in the quarters ahead. The company intends to place an application for patisiran in front of the Food and Drug Administration before the end of the year.

An approval and commercial launch would trigger milestone payments from Sanofi that Alnylam can use to accelerate development of several more candidates in late-stage development, including a program for givosiran, a rare-liver-disease drug that could be ready to submit an FDA application next year.

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