Jan 29 (Reuters) - Gilead Sciences said on Monday it has raised its stake in Arcus Biosciences to 33% and expanded its presence in the drug developer's board to three, deepening their collaboration in developing cancer drugs.

It made an equity investment of $320 million, buying Arcus stock at $21 per share, a 37.3% premium to its last closing price. Shares of Arcus rose 11.8% to $17.2 after the bell.

Gilead said its Chief Commercial Officer Johanna Mercier will join Arcus' board. The company had previously held a 20% stake in Arcus, according to a brokerage note by Jefferies.

The two companies said they would discontinue a late-stage trial testing their candidate domvanalimab in combination with another experimental drug zimberelimab to treat a type of non-small cell lung cancer.

Domvanalimab belongs to a class of treatments known as anti-TIGIT that targets a protein receptor on immune cells that acts as a brake on the immune response.

The move comes as the companies reprioritize the joint domvanalimab development program to focus on advancing two late-stage trials testing the drug in treating lung cancer and gastrointestinal cancer.

The trials are expected to be fully enrolled by the end of the year. A planned late-stage study in pancreatic cancer evaluating investigational drug quemliclustat will also become an Arcus independent study, the companies said. (Reporting by Pratik Jain in Bengaluru; Editing by Arun Koyyur)