FRANKFURT, March 20 (Reuters) - Swiss drugmaker Novartis

on Friday agreed to buy a breast cancer drug candidate

for up to $3 billion from U.S. biotech firm Synnovation

Therapeutics, adding a targeted therapy to its pipeline of

cancer drugs.

The company will pay $2 billion upfront and up to $1 billion

that is contingent on further development achievements as part

of the deal.

The experimental drug, SNV4818, belongs to a class of

selective PI3Kα inhibitors, a new approach for the treatment of

a type of breast cancer known as HR positive/HER2 negative and

potentially other solid tumours.

The acquisition adds to a growing pipeline of targeted

cancer therapies, including a radioligand therapy candidate,

that Novartis is already testing. SNV4818 is currently in

early-stage trials and has shown promising activity against

tumors in lab studies, Novartis said.

Synnovation's drug targets only the mutated form of PI3Kα,

an enzyme that often malfunctions in breast and other forms of

cancer, while sparing the normal version found in healthy cells.

And it aims to avoid the side effects seen with existing

PI3Kα-inhibiting therapies.

"While mutated PI3Kα is a well-established driver in

HR+/HER2- breast cancer, there remains a challenge in achieving

effective pathway inhibition with a tolerable therapeutic

profile," said Shreeram Aradhye, the drugmaker's chief medical

officer.

Novartis expects the deal to close in the first half of this

year.