The drug in question is the immunotherapy Keytruda (famous for being used to treat President Jimmy Carter’s melanoma). It was being tested in patients with a specific type of lung cancer called advanced non-small cell lung cancer (NSCLC) who also had high levels of a biological marker called PD-L1 (the treatment is most effective in patients whose tumors have that protein).

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Keytruda met its main goals in the clinical trial, according to Merck, improving previously untreated patients’ overall survival rates and preventing their disease from worsening. Merck’s drug proved sufficiently superior to chemotherapy as a first-response treatment that an independent committee overseeing the study recommended it be halted and that all the participants be given the opportunity to receive Keytruda.

Merck didn’t release detailed data in its press release, but promised that the information would be unveiled during an “upcoming medical meeting.”

This is particularly good news for Merck given the ongoing dominance of Bristol-Myers Squibb’s (BMY) competing cancer immunotherapy Opdivo. That treatment, despite coming to market three months after Keytruda in 2014, garnered about 66% more in 2015 sales than its rival did.

Both Keytruda and Opdivo are cleared to treat a number of cancers, including melanoma and lung cancer, and are being tested in dozens of other cancers. But Keytruda can only be used as a secondary treatment in NSCLC after chemotherapy has already failed, as well as in some patients who haven’t responded to other types of treatment.

A first-line approval could go a long way toward helping Merck play catch-up to Bristol-Myers — or so the company hopes. Its rival is presenting its own first-response treatment data, and if they’re good enough, Merck’s boost could be short-lived.

Merck shares closed up 2.5% on Thursday.