GlaxoSmithKline just agreed to acquire the cancer-drug maker Tesaro for $5.1 billion in a bid to bulk up its cancer pipeline.

Tesaro makes a drug called Zejula, which is used to treat ovarian cancer.

GSK has been working to refresh its research-and-development strategy — in July it made a $300 million investment in the consumer-genetics company 23andMe.

GlaxoSmithKline is getting deeper into the development of cancer drugs.

On Monday, the UK-based pharma giant said it had agreed to acquire Tesaro, a drugmaker with a treatment for ovarian cancer, for $5.1 billion.

Tesaro was up 60% on the news before markets opened Monday, while GSK was down 6%.

GSK has been working to refresh its research-and-development strategy. In 2017, GSK brought on Hal Barron, a former Genentech and Calico executive, as its chief scientific officer and president of R&D.

As part of that, the company made a $300 million investment in the consumer-genetics company 23andme. GSK also said in July that it planned to focus its research efforts on developing new treatments that act on the body's immune system.

Read more: Why the pharma giant GSK just made a $300 million bet on 23andMe's approach to finding new medicines

Tesaro makes a cancer drug called Zejula, which is used to treat ovarian cancer.

A pill taken once a day, Zejula is part of a group of cancer drugs called PARP inhibitors. Essentially, they block an enzyme that our cells use to repair DNA. That repair system is broken in certain kinds of cancer, allowing cancer cells to thrive, so blocking it is critical.

"Our strong belief is that PARP inhibitors are important medicines that have been underappreciated in terms of the impact they can have on cancer patients," Barron said said in a press release. "We are optimistic that Zejula will demonstrate benefit in patients with ovarian cancer beyond those who are BRCA-positive as front-line treatment."

Pfizer acquired a PARP inhibitor in its deal for Medivation, while Clovis Oncology makes Rubraca and AstraZeneca has Lynparza.

PJT Partners and Bank of America Merrill Lynch advised GSK, while Citi and Centerview advised Tesaro on the deal.