(Reuters) -Britain’s GlaxoSmithKline has agreed to buy California-based biopharmaceutical company Sierra Oncology in a cash deal valued at $1.9 billion, the companies said on Wednesday, as it seeks to bolster its blood cancer business.

Shareholders in Sierra, which focuses on targeted therapies for the treatment of rare forms of cancer, will receive $55 per share of common stock in cash, GSK said.

That’s a 39% premium to Tuesday’s closing price and about two thirds more than the volume-weighted average price (VWAP) over the last 30 trading days, it said.

The deal comes as Sierra prepares to apply in the second quarter for U.S. marketing approval for its experimental drug momelotinib, used to treat anaemic patients with a type of bone marrow cancer.

Data from a late-stage clinical trial showed in January it was successful in reducing disease symptoms and also cut patients’ dependence on blood transfusions.

The acquisition will complement GSK’s multiple myeloma treatment, Blenrep, GSK said. Myeloma is a type of blood cancer that develops from cells in the bone marrow called plasma cells.

(Reporting by Yadarisa Shabong in Bengaluru and Natalie Grover in LondonEditing by Josephine Mason and Mark Potter)