Almost £1.7bn was wiped from the value of GSK PLC (LSE:GSK, NYSE:GSK) in opening deals after the drug developer revealed a late-stage study failed to meet its main goal.
Blenrep was deemed no better than the current standard of care in helping people with hard-to-treat multiple myeloma, a type of bone marrow cancer.
The DREAMM-3 phase III evaluation of the treatment was what is called a superiority trial.
GSK said its data will be shared with the various regulatory bodies, while additional studies will continue.
Blenrep received approval from drug watchdogs in Europe and the US to be used in multiple myeloma patients who have effectively exhausted the current treatment regimens.
How the latest setback affects sales, expected to be in the region of £1.5bn for 2024, remains to be seen.
However, the market took pre-emptive action as the stock was marked down 3% to £14.03.