Shares in Irish pharmaceutical giant Shire surged after Japan's Takeda said it is considering making a takeover approach for the €37.5bn valued firm.
Takeda said that its consideration of an offer is at a "preliminary and exploratory stage", and no approach has been made to Shire's board.
"There can be no certainty that an approach, if made, will lead to any transaction," the firm said.
The FTSE 100 firm's shares rocketed on the news, rising over 20% to 3,708p.
Takeda said a potential transaction with Shire presents an opportunity to create a "truly global, value-based Japanese biopharmaceutical leader", strengthening its core oncology, gastrointestinal and neuroscience offerings.
In addition, a tie-up would help realise the Japanese company's R&D strategy, drive financial value and allow it to exploit further opportunities in the US.
Takeda said: "Clearly defined strategic and financial objectives are core to Takeda's disciplined approach to acquisitions, including in relation to its dividend policy and credit rating, which are well-established.
"Any potential offer for Shire, if made, would have to align with this strict investment criteria."
According to UK takeover rules, Takeda must now either make an offer or walk away by April 25.
Takeda, which was founded in 1781 and employs 30,000 people, has a strong presence in emerging markets and operates in more than 70 countries.
If a deal were to be struck, it would see the hunter become the hunted after Shire itself went on the acquisition trail only two years ago when it bought Baxalta for $32bn (€25.84bn).
Last year, Shire's revenues doubled following the takeover to $3.57bn (€2.88bn), the bulk of which came from the Baxalta business.
When stripped of legacy Baxalta sales, revenues rose only 11% to $1.8bn (€1.59bn).