Celgene Corp. said on Monday it would pay about $9 billion in cash to acquire the rest of Juno Therapeutics Inc. and gain access to Juno's experimental gene therapy to treat cancer.

The $9 billion represents an offer $87 per share to Juno's shareholders and the deal, agreed by both boards, is expected to close in the first quarter of 2018.

Shares of Juno rose 26.8 percent to $86.01 in premarket trading. Shares of Celgene were marginally up.

The acquisition will add JCAR017, Juno's experimental treatment for a type of blood cancer, to Celgene's lymphoma program.

The drug is expected to be approved in 2019 and could bring in peak sales of about $3 billion worldwide, the companies said.

In 2015, Celgene paid $93 per Juno share for 9.7 percent of the company.

J.P. Morgan Securities LLC is the financial adviser for Celgene and Morgan Stanley & Co for Juno.

Proskauer Rose LLP and Hogan Lovells will be the legal counsel for Celgene and Skadden, Arps, Slate, Meagher and Flom LLP for Juno.