What happened

Shares of Alnylam Pharmaceuticals (NASDAQ:ALNY) were up 19% at 12:04 p.m. EDT on Monday after rival Pfizer (NYSE:PFE) released data for its transthyretin amyloid (ATTR) drug tafamidis at the ESC Congress 2018, which were also published in the New England Journal of Medicine. Earlier this month, Alnylam got its ATTR drug, Onpattro, approved by the Food and Drug Administration. Shares of Ionis Pharmaceuticals (NASDAQ:IONS) and Akcea Therapeutics (NASDAQ:AKCA), which are jointly developing another ATTR drug, Tegsedi, are up 10% and 2.6% respectively.

So what

Investors already knew the clinical trial testing tafamidis in patients with the cardiomyopathy version of ATTR was successful, so today's reaction by investors in Alnylam, Ionis, and Akcea highlights the age-old biotech rule that the devil is usually in the details.

Pfizer's headline results were certainly solid enough to get tafamidis approved: The drug reduced the risk of mortality by 30% and the rate of cardiovascular-related hospitalizations by 32% compared to placebo. But the mortality curves don't start separating until 18 months, leaving open the possibility that Alnylam or Ionis/Akcea could show their drugs work faster given the different mechanism of action.

Investors in Pfizer's competitors can also rejoice in the lack of data in patients with ATTR due to a mutation in transthyretin (TTR), which is the population that Alnylam's Onpattro and Ionis' and Akcea's Tegsedi were tested in. Just 24% of the patients in Pfizer's trial had the mutant version, making it difficult for Pfizer to show that the drug works specifically in those patients; the rest had the normal "wild type" protein.

Doctor and patient sitting at a table

Image source: Getty Images.

Of course, all this competition is theoretical at this point since Onpattro is approved for patients with polyneuropathy symptoms of ATTR (the TTR protein aggregates in the nervous system). Alnylam does have some data showing it can help patients with cardiomyopathy (TTR protein aggregates in the heart), but the FDA didn't allow the company to put it on the label. In the short term, the data affect Ionis Therapeutics and Akcea Therapeutics even less since they don't have any appreciable data for Tegsedi in patients with cardiomyopathy.

Now what

Alnylam will likely try to break into the cardiomyopathy population as well as test the drug on the wild-type population with its follow-on drug ALN-TTRsc02. Ionis also has a follow-on drug that it could expand into those populations as well.

With Pfizer having set the bar at an attainable level, the smaller biotechs have a fighting chance to compete, but it'll be a few years before we know one way or the other.

Brian Orelli 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.