Shares of Takeda Pharmaceutical Co. fell the most in nine years after the firm disclosed it is considering a bid for Shire PLC that could approach $50 billion (about ?5.3 trillion), which would be the Japanese company¡¯s biggest takeover ever.

The decline in early Tokyo trading shaved $3 billion from Takeda¡¯s market cap. Coupled with a rally in Shire¡¯s stock on the news, the valuation gap between the two companies widened by almost $6.5 billion, posing a bigger financial challenge for Takeda if it decides to go forward with an offer.

¡°Takeda is just desperate to beef up its pipeline, and they¡¯ve been doing small bits of acquisitions on the biotech side,¡± said Fumiyoshi Sakai, a Tokyo-based analyst at Credit Suisse Securities. ¡°But how they are going to finance $40-some billion? That¡¯s another one.¡±