Biotech Dealmaking Spree Sparks Torrent of Shareholder Lawsuits

A high volume of mergers in the biotech space is giving way to a flow of shareholder lawsuits seeking to block or rescind the tie-ups.

These securities suits are drawing willing plaintiffs despite the fact that such cases are rarely successful in preventing an announced merger from being completed or reversing an already approved deal. They’re amassing as a years-long run-up in dealmaking begins to ebb.

Among the past year’s 10 biggest biotech mergers, half of the companies involved faced lawsuits related to their M&A activity, according to data compiled by Bloomberg. The suits have included litigation against Seagen Inc. ...