Ropes & Gray, Hogan Lovells, and Shearman & Sterling have taken the lead roles on a $5.1 billion deal in which London-based GlaxoSmithKline (GSK) will acquire Waltham, Massachusetts-based biopharmaceutical firm TESARO, Inc.

The deal is expected to strengthen GSK’s presence in cancer treatment and the treatment of tumors—an area in which TESARO is a pioneer. One of TESARO’s trademark products is the drug Zejula, which is approved for use in the U.S. and Europe and has revolutionized the treatment of ovarian cancer.

In a statement, TESARO described the drug as a treatment for adult patients with recurrent ovarian cancer who are undergoing chemotherapy and described a potential expanded use for the drug, noting that clinical trials are underway.

Leading the charge on the deal for Ropes & Gray were securities and public company partners Christopher Comeau and Paul Kinsella, life sciences partner Al Cacozza, health care partner Eve Brunts, litigation and enforcement partners Peter Welsh and Ama Adams and lawyers in several other practice areas, including tax, benefits and antitrust law.

Hogan Lovells partners Asher Rubin and William Intner and senior associate Nick Hoover also advised TESARO.

GSK took legal advice from a large team of Shearman & Sterling lawyers, including M&A partners George Casey and George Karafotias, IP transactional lawyer Jordan Altman, antitrust attorney Jessica Delbaum, and compensation, governance and ERISA lawyer Doreen Lilienfeld.

Slaughter and May advised on the acquisition facility.

The TESARO-GSK deal is the latest high-profile transaction for Ropes & Gray. In September, the firm said it was advising Shanghai-based biopharma firm Zai Lab in a joint venture for the commercialization of Novocure’s oncology assets. And in October, it said it was advising Bain Capital in a $350 million venture with Pfizer Inc. to form Cerevel Therapeutics.

As the demand for expert counsel in the life sciences space has grown, Ropes & Gray has added bench strength, notably with the hiring of partner Eric Wu from Johnson & Johnson in 2018 and the recruitment of counsel Beth Weinman from the chief counsel office of the Food and Drug Administration in October 2018. Earlier this year, the firm added Filko Prugo as partner and chair of the firm’s life sciences IP litigation practice and Charlotte Jacobson as a litigation partner.