Merck to Buy Rare-Disease Firm Acceleron for $11.5 Billion (2)

Merck & Co. agreed to buy Acceleron Pharma Inc. for about $11.5 billion, building out its portfolio of therapies to treat rare diseases.

Acceleron shareholders will get $180 a share in cash, a 34% premium over the price at the end of last month but below the stock’s intraday highs this week. The shares began soaring in mid-September, and Bloomberg reported Sept. 24 that the company was in advanced sale talks.

Merck has faced pressure to expand its sales beyond Keytruda, a blockbuster cancer drug that accounts for more than a third of its revenue. It is among several companies ...