Investors have to register when they own more then 5% of a public company. This is visible to everyone. Furthermore investors who own more then 10% have to publicly file when they increase or decrease their position. They also have to declare whether or not it is their intent to gain majority control.
Because of this a hostile takeover is unlikely as these announcements would created a bidding war, and with several big pharmas potentially interested it would likely be easier and cheaper to negotiate for a buyout privately.
Hostile takeovers usually only occur when only one group sees value in acquiring a company due to liquidation value or synergies exclusive to the acquiring company
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