Merck & Co Inc's blockbuster drug Keytruda in combination with two chemotherapy drugs was successful as a first line treatment for lung cancer, results from a key late-stage study showed on Tuesday.

The U.S. drugmaker's shares rose 2.7 percent to $60.25 in premarket trading.

The results present a challenge to Swiss drugmaker Roche and Merck's U.S. rival Bristol-Myers Squibb Co, both of which are developing key lung cancer combination treatments of their own.

Roche said last month its immunotherapy Tecentriq, when combined with other drugs, doubled the percentage of lung cancer patients who survived a year without their disease advancing.

Roche's shares fell 2.5 percent on Tuesday, while shares of Bristol-Myers dipped nearly 2 percent in U.S. premarket trading.

The Merck study tested a cocktail of Keytruda, Eli Lilly's Alimta and a standard chemotherapy as an initial treatment for patients with a type of non-small-cell lung cancer, a common form of the disease.

The study met its main goals of preventing cancer from worsening and extending patients' overall survival.

Keytruda is already approved to treat several types of cancer including lung cancer, both as a single agent and in combination with other drugs.