Britain's AstraZeneca PLC agreed to pay Japanese drugmaker Daiichi Sankyo Co. up to $6.9 billion for a piece of a promising cancer treatment in its biggest deal in over a decade as it aims to become a global oncology powerhouse.

AstraZeneca will pay Daiichi Sankyo $1.35 billion upfront to jointly develop and commercialize the cancer therapy trastuzumab deruxtecan, with as much as $5.6 billion in additional payments subject to sales milestones and other contingencies, the companies said late Thursday. They will also equally split development and commercialization costs.

The British company said it will fund the transaction partly through a share sale of up to $3.5 billion. Daiichi Sankyo shares surged 15.9 percent — the stock's daily limit — to an all-time high in Tokyo trading Friday.