By Tamara Mathias and Rebecca Spalding

(Reuters) – Alexion Pharmaceuticals Inc said on Friday its board of directors had unanimously rejected hedge fund Elliott Management’s push for a “proactive sale” process of the entire company because it would not be in the best interest of shareholders.

Alexion has been fighting to maintain its leadership in treating certain rare blood disorders, and has embarked on a string of acquisitions to boost its pipeline of rare disease drugs. In October, it agreed to buy rival Achillion Pharmaceuticals Inc for about $930 million.

Alexion, with a market capitalization of about $24 billion, said it took into account the hedge fund’s views but concluded it was “highly unusual, if not unprecedented” for a company of its size to proactively launch a process to sell itself.

“To eliminate confusion and inaccurate information in the marketplace, to date, Alexion has not received any indications of interest to acquire the company nor have we rejected any such inbound proposals,” the company said.

The most notable part of Alexion’s announcement is that it has not received any indications of takeover interest, Stifel analyst Paul Matteis said. “Putting this in context, a component of the Alexion investor bull case is the potential for M&A.”

Shares of the U.S. drugmaker rose 5.1% to $112.98 shortly after midday in New York. As of Friday, the shares have risen about 16.5% this year, underperforming the more than 23.6% gain in the Nasdaq biotechnology index.

“Shares are rising because this issue between Alexion and Elliott might flush out prospective buyers,” Oppenheimer & Co analyst Hartaj Singh said.

“There has been frustration among Alexion shareholders about share price performance.”

With U.S. market exclusivity for its best-selling drug Soliris under threat, Alexion has been pushing to convert patients to its newer successor drug Ultomiris, and add approvals for more indications to the drug’s label.Alexion’s brush with Elliott is its second with the hedge fund, which in 2017 pushed for changes at the company. It supported the 2018 appointment of Deborah Dunsire, now chief executive of Danish drugmaker H. Lundbeck A/S , to the board.Alexion’s board also includes seasoned dealmaker Felix Baker, co-managing member of hedge fund Baker Bros Advisors LP. He joined the board when Alexion paid $8.4 billion to acquire Synageva BioPharma Corp where he was a director. Baker also served on the board of Genomic Health, which Exact Sciences bought earlier this year for about $2.8 billion.

Alexion said on Friday that since 2017, it has added five new directors with input from investors including Elliott.

(Reporting by Tamara Mathias in Bengaluru and Rebecca Spalding in New York; Editing by Arun Koyyur, Maju Samuel and Richard Chang)