What happened

Shares of Alnylam Pharmaceuticals (ALNY -1.93%) are tanking this week, falling 18.4% as of the market close on Thursday, according to data from S&P Global Market Intelligence. The decline came primarily after the company announced its third-quarter results on Thursday.

Alnylam reported third-quarter revenue of $167 million. Although this figure reflected strong year-over-year growth of 68%, it came in well below the consensus analysts' estimate of $218.7 million. The company posted an adjusted net loss of $1.51 per share, a little better than the loss of $1.57 expected by analysts.

In addition, Alnylam announced that CEO John Maraganore will step down at the end of 2021. Maraganore joined the company as its founding CEO in 2002. He will be replaced by Yvonne Greenstreet, who currently is Alnylam's president and chief operating officer. 

A scientist looking through a microscope.

Image source: Getty Images.

So what

Growth for all three of Alnylam's rare-disease drugs on the market experienced slowdowns in the third quarter. The company reported third-quarter sales of Onpattro rose 6% sequentially to $120 million, a growth rate that was halved from the previous quarter. Sales of Givlaari climbed 4% sequentially to $32 million, much slower than the 24% sequential increase in the second quarter. 

The biggest drop-off was for Oxlumo. Sales for the drug fell 9% from the previous quarter to $15 million. Alnylam attributed this decline to the transition of commercial patients to quarterly maintenance dose regiments from a monthly dose.

Maraganore's departure also came as a surprise to investors. The longtime CEO said, "I have decided that this is the right time to transition my leadership at year end to focus my next chapter on helping other entrepreneurs and companies advance new frontiers of medicine."

Now what

The biotech stock might not stay down for too long. Alnylam plans to report full results from its phase 3 study of lumasiran at the American Society of Nephrology Kidney Week in November. It's scheduled to announce additional results from the phase 1 study of zilebesiran in treating hypertension later next month. The company also intends to provide full 18-month endpoint and safety results from its phase 3 study of vutrisiran early next year.