Bristol-Myers Squibb (BMY) - Get Report  shares edged down in the Thursday premarket after a Phase III trial of a proposed new drug to battle GBM, a rare form of brain cancer, failed to show meaningful results.

The New York pharma giant reported that Opdivo "failed to demonstrate a statistically valid increase in progression-free survival, one of the two primary endpoints."

The new drug failed to show any measurable improvement in patients with a particularly aggressive form of newly diagnosed glioblastoma multiforme compared with others treated with the current standard of care, which involves temozolomide and radiation therapy.

But the data-monitoring committee overseeing the drug trial -- Phase 3 CheckMate - 548 -- has also recommended that the tests continue so that the overall survival rates among patients can be evaluated.

GBM currently strikes 10 of every 100,000 people globally, with a five-year survival rate of less than 5%.

"[We] are continuing to evaluate the benefit the addition of Opdivo to the standard of care treatment regimen may bring to patients suffering from GBM, an extremely aggressive and difficult disease to treat," said Fouad Namouni, a physician who heads oncology development at Bristol-Myers Squibb, in a statement.