CytomX extends deal with Bristol-Myers for $3.8 billion

Shares of South San Francisco biotech company CytomX Therapeutics soared Monday by the most since October 2015 after the drugmaker extended its partnership with Bristol-Myers Squibb in a deal worth as much as $3.8 billion.

Bristol-Myers will pay CytomX $200 million initially, will provide research funds, and has the option for exclusive worldwide rights to develop and commercialize as many as six cancer and two non-cancer treatments, according to a statement from the companies on Monday.

CytomX is eligible for as much as $448 million in additional payments for each target tied to development, regulatory and sales milestones.

CytomX makes a type of drug called a Probody therapeutic, which the company says is safer than some other cancer treatments because it’s only active when it is close to a tumor microenvironment, thus avoiding harm to healthy tissues.

The New York pharmaceutical giant is competing with other major drugmakers to extend its foothold in the cancer market, and uses partnerships with smaller biotechnology companies like CytomX to stock its pipeline of drugs.