What happened

Shares of Apellis Pharmaceuticals (APLS -0.65%), a biopharmaceutical company focused on rare diseases, are sliding lower on Friday. Investors responding to conflicting clinical trial data for the company's experimental blindness prevention drug pushed the stock 47.94% lower as of 10:25 a.m. EDT on Friday.

So what 

Apellis earned Food and Drug Administration approval for its first drug, Empaveli, this May so there's still a lot riding on pegcetacoplan, the next potential new drug emerging from the company's pipeline. Unfortunately, pegcetacoplan produced clinical trial results that weren't as convincing as investors had hoped.

Frustrated investor checking stocks on a computer.

Image source: Getty Images.

A pair of identical phase 3 studies named Oaks and Derby tested injections of pegcetacoplan on over 1,200 patients with geographic atrophy. In the Oaks trial, a year of treatment with pegcetacoplan significantly reduced the growth of retinal lesions compared to a placebo. Unfortunately, reductions recorded in the Derby trial weren't strong enough to be considered statistically significant.

Now what

Geographic atrophy is an advanced and aggressive form of age-related macular degeneration, or AMD. Effective treatments that prevent the progression of AMD have been generating blockbuster sales for years, but there still aren't any treatments approved to treat geographic atrophy specifically. 

Results from the Derby trial were close enough to a level considered statistically significant that Apellis Pharmaceuticals is going to forge ahead with pegcetacoplan. The biotech plans to submit a new drug application to the FDA for the treatment of geographic atrophy in the first half of 2022.