Biopharmaceutical company GSK plc (LSE/NYSE: GSK) announced on Monday that it has entered an agreement to acquire IDRx Inc, a Boston-based clinical-stage biopharmaceutical company, for up to USD1.15bn.

The acquisition includes IDRX-42, a selective KIT tyrosine kinase inhibitor (TKI) targeting gastrointestinal stromal tumours (GIST). GSK will pay USD1bn upfront, with an additional USD150m tied to regulatory milestones.

IDRX-42 is designed to address all primary and secondary KIT mutations that drive GIST progression, offering potential improvements in efficacy and tolerability over existing therapies. Recent phase I/Ib trial data demonstrated a 53% objective response rate in patients treated after one prior therapy, with a manageable safety profile.

GSK's expanding gastrointestinal cancer portfolio, which includes assets like dostarlimab and GSK5764227, underscores its focus on targeted mechanisms to address unmet medical needs. The acquisition aligns with GSK's growth ambitions through 2031 and beyond.

GIST is the most common subtype of soft tissue sarcoma, affecting up to 120,000 patients globally each year. Mutations in the KIT gene drive 80% of cases, with most first-line patients developing resistance mutations that lead to relapse. IDRX-42 has FDA Fast Track and Orphan Drug designations, highlighting its potential to fill critical gaps in treatment options.

The transaction, subject to regulatory approvals under the Hart-Scott-Rodino Act, also includes milestone payments and royalties to Merck KGaA, Darmstadt, Germany, for IDRX-42. Legal and financial advisory roles were provided by Centerview Partners, Goodwin Procter, and Leerink Partners.