The proposed transaction will significantly strengthen GSK’s pharmaceutical business, accelerating the build of GSK’s pipeline and commercial capability in oncology (Photo: Igor Golovniov/SOPA Images/LightRocket via Getty Images).

GlaxoSmithKline Plc and Tesaro Inc have announced on Monday (3) that the companies have entered into a definitive agreement pursuant to which GSK will acquire Tesaro, an oncology-focused company based in Waltham, Massachusetts for approximately four billion pounds.

The proposed transaction will significantly strengthen GSK’s pharmaceutical business, accelerating the build of GSK’s pipeline and commercial capability in oncology.

Tesaro is a commercial-stage biopharmaceutical company, with a major marketed product, zejula (niraparib), an oral poly ADP ribose polymerase (PARP) inhibitor currently approved for use in ovarian cancer. PARP inhibitors are transforming the treatment of ovarian cancer, notably demonstrating marked clinical benefit in patients with and without germline mutations in a BRCA gene (gBRCA).

Zejula is currently approved in the US and Europe as a treatment for adult patients with recurrent ovarian cancer who are in response to platinum-based chemotherapy, regardless of BRCA mutation or biomarker status.

Clinical trials to assess the use of Zejula in “all-comers” patient populations, as a monotherapy and in combinations, for the significantly larger opportunity of first-line maintenance treatment of ovarian cancer are also underway.

These ongoing trials are evaluating the potential benefit of Zejula in patients who carry gBRCA mutations as well as the larger population of patients without gBRCA mutations whose tumours are HRD-positive and HRD-negative. Results from the first of these studies, PRIMA, are expected to be available in the second half of 2019.

GSK also believes PARP inhibitors offer significant opportunities for use in the treatment of multiple cancer types. In addition to ovarian cancer, Zejula is currently being investigated for use as a possible treatment in lung, breast and prostate cancer, both as a monotherapy and in combination with other medicines, including with Tesaro’s own anti-PD-1 antibody (dostarlimab, formerly known as TSR-042).

In addition to Zejula, Tesaro has several oncology assets in its pipeline including antibodies directed against PD-1, TIM-3, and LAG-3 targets.

Emma Walmsley, Chief Executive Officer, GSK, said, “the acquisition of Tesaro will strengthen our pharmaceuticals business by accelerating the build of our oncology pipeline and commercial footprint, along with providing access to new scientific capabilities. This combination will support our aim to deliver long-term sustainable growth and is consistent with our capital allocation priorities. We look forward to working with Tesaro’s talented team to bring valuable new medicines to patients.”

The acquisition price of $75 per share in cash represents a 110 per cent premium to TESARO’s 30-day volume weighted average price of $35.67 and an aggregate consideration of approximately $5.1 bn (£4.0bn) including the assumption of Tesaro’s net debt.

Zejula’s revenues in its current approved indication as second-line maintenance treatment for ovarian cancer were $166 million for the nine months ended September 30, 2018.