Activist investor Carl Icahn reported a 12.63 percent stake in medical device maker Hologic Inc., prompting the company to adopt a shareholder rights plan to protect itself from hostile takeovers.

In a filing with the U.S. Securities and Exchange Commission, Icahn said he, along with his affiliates, intend to discuss the possibility of board representation and ways to improve shareholder value with Hologic's management.

Hologic's rights plan will be exercisable if a person or group acquires 10 percent or more of the company's common stock.

Hologic shares were up 7 percent at $23.85 in premarket trading.