One failed study shows just how fiercely competitive a new field of cancer therapy is

Shares of Bristol-Myers Squibb were hit hard in pre-market trading Friday after news that its blockbuster cancer drug failed a key clinical trial.

The drug, called Opdivo, is one of a new set of drugs called immunotherapy. The drug targets the programmed cell death 1 (or PD-1) receptor to essentially take the "foot off the brake pedal" in the immune system, so that the immune system can go after the caner cells.

The trial was for patients with previously untreated non-small cell lung cancer, a common form of lung cancer.

"CheckMate -026 was designed to answer the question of the benefit of Opdivo monotherapy in a broad patient population. Unfortunately, this trial did not meet its primary endpoint of progression-free survival in patients whose tumors expressed PD-L1 at ≥ 5%," BMS said in a statement.

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Opdivo, which has already been approved to treat other forms of cancer, has been a big hit for BMS, bringing in $840 million in second-quarter sales alone.

In comparison, its main anti-PD-1 immunotherapy competition Keytruda, made by Merck, made $314 million in sales the same quarter.

However, in June, Keytruda succeeded in its trial that was designed a bit differently treating patients with non-small cell lung cancer who hadn't received any prior treatments.

Merck was up as much as 11% Friday morning on the news of BMS's trial.

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