Bristol-Myers Squibb (BMS) has decided against pursuing early FDA approval for its big immunotherapy candidate Opdivo in lung cancer treatment.

The filing would have seen BMS seeking approval for its drug in combination with another immunotherapy called Yervoy (ipilimumab) for first line treatment of lung cancer.

Both Opdivo and Yervoy work by activating immune cells to the presence of cancer, helping them detect and destroy cancer cells.

Unfortunately for BMS, the decision puts it further behind its rival Merck & Co’s Keytruda (pembrolizumab) – a drug that works in the same way as Opdivo.

In August of last year, Opdivo failed in a major first-line trial in lung cancer, giving Keytruda the edge in their ongoing battle. Results to the Checkmate-026 phase 3 trial, revealed at last year’s European Society for Medical Oncology (ESMO) meeting, revealed the drug had not met its primary endpoint of improved progression-free survival in patients with advanced non-small cell lung cancer.

Keytruda’s advantage was bolstered when it was given approval as a first-line lung cancer treatment two months later.

Since then, BMS shares have gradually dropped while Merck’s have steadily risen and have now overtaken.