As Seattle Genetics Inc. rallies on a successful breast cancer study Monday, the biotech’s largest holder, Baker Bros. Advisors LP, stands to gain nearly $730 million on the day from its stake.

The investment firm founded by Felix and Julian Baker made a big bet in the company, their biggest in fact, with a 29% stake, as of June 30, according to data compiled by Bloomberg. That stake is worth roughly $5 billion today after tucatinib -- an experimental therapy Seattle Genetics acquired for more than $400 million last year -- surprised investors by slowing the spread cancer and extending patients’ lives. Even more surprisingly, it had an effect on patients whose cancer had spread to their brains.

Baker Bros. has been invested in the company for over 15 years, and Felix Baker is a lead director for the biotech. Today Seattle Genetics makes up over 28% of Baker Bros.’s $15.5 billion in assets.

The stock rose as much as 17% to a record high of $101.95 intraday. Twelve analysts that follow the company rate it the equivalent of a buy, five rate it a hold and one rates it a sell. With an average price target of $87, some analyst target raises are likely in the near future.

This article was provided by Bloomberg News.