(Reuters) -British drugmaker GSK said on Monday that it would pay up to $1.15 billion to buy Boston-based biopharmaceutical firm IDRx, which is developing a treatment for a rare type of tumour. IDRx,

GSK (NYSE:GSK) finalized the deal to acquire Boston-based, clinical-stage biopharmaceutical company—IDRx for a total of up to $1.15 billion cash consideration. Under the agreement signed by both companies,

GSK plc (LSE/NYSE: GSK) and IDRx, Inc. (IDRx) today announced that they have entered into an agreement under which GSK will acquire IDRx, a Boston-based, clinical-stage biopharmaceutical company dedicated to developing precision therapeutics for the treatment of GIST.

This morning, the UK pharma group confirmed it had signed an agreement to buy privately-held IDRx for $1 billion upfront, with another $150 million in payments to the biotech's shareholders if its pipeline delivered as expected.

GSK's $1 billion acquisition of IDRx includes IDRX-42, a precision therapy for GIST. Phase 1/1b trial shows 53% ORR in early treatment stages.

GSK is reportedly in late-stage negotiations about a $1 billion deal to acquire IDRx and its experimental targeted therapy for a form of rare gastrointestinal stromal tumour (GIST).

Under the agreement, GSK will pay $1billion upfront to acquire the Massachussetts-based firm, followed by up to $150million in 'success-based' milestone payments.