Following weeks of speculation Pfizer has stepped forward with a $14-billion bid for Medivation, beating Sanofi and other suitors to the finish line in a move designed to boost its oncology portfolio.

The drug giant has announced a definitive merger agreement under which it will acquire the US biopharma, which is focused on developing and commercialising small molecules for oncology, for $81.50 a share in cash, to be financed with existing funds.

The boards of directors of both parties have already unanimously approved the deal, which is expected to be immediately accretive to Pfizer's adjusted diluted earnings per share upon closing, around $0.05 accretive in the first full year after close, with additional accretion and growth anticipated thereafter.

"The proposed acquisition of Medivation is expected to immediately accelerate revenue growth and drive overall earnings growth potential for Pfizer," said Ian Read, the firm's chairman and chief executive. "The addition of Medivation will strengthen Pfizer's Innovative Health business and accelerate its pathway to a leadership position in oncology, one of our key focus areas, which we believe will drive greater growth and scale of that business over the long-term."

The move gives Pfizer access to prostate cancer drug Xtandi (enzalutamide), an androgen receptor inhibitor that blocks multiple steps in the androgen receptor signalling pathway within the tumour cell, which generated global sales of around $2.2 billion over the past four quarters, as recorded by Medivation's partner Astellas Pharma.

The drug is currently being tested in Phase III studies in non-metastatic prostate cancer and hormone-sensitive prostate cancer, as well as Phase II trials for the potential treatment of advanced breast cancer and hepatocellular carcinoma.

Medivation also has a "promising, wholly-owned, late-stage oncology pipeline", which includes two development-stage oncology assets, talazoparib and pidilizumab. Talazoparib is currently in a Phase III study for the treatment of BRCA-mutated breast cancer and, according to Pfizer, has the potential to be a highly potent PARP inhibitor potentially efficacious across several additional tumours. Pidilizumab is an immuno-oncology asset being developed for diffuse large B-cell lymphoma and other haematologic malignancies.

Commenting on the move, Michael Jewell, healthcare partner at Cavendish Corporate Finance, said: "This deal, which is one of the biggest in the oncology field, supports the trend that companies with innovative medicines, such as Medivation's cancer drug Xtandi, and experimental tumour cells drug Talazoparib, make businesses attractive takeover targets".