Merck & Co (MRK - Get Report) shares edged higher Monday after the drugmaker won approval for the sale of its blockbuster lung cancer treatment in China.

Merck's anti-PD-1 therapy, which treats patients with a certain form of lung cancer in combination with chemotherapy, is better known by its brand name Keytruda. The drug, Merck's top selling product last year, was approved for sale in China as a first-line treatment, where there are nearly 782,000 new cases recorded each and every year, most of which are treatable with the Keytruda combination.

"This approval represents a key advance in a country with a high incidence of lung cancer, and where significant progress for the first-line treatment of this devastating disease has been very limited over a number of years," said Dr. Roy Baynes, senior vice president and head of global clinical development and chief medical officer at Merck Research Laboratories. "This also means that, based on the results of KEYNOTE-189, KEYTRUDA in combination with chemotherapy has now been approved in the U.S., Europe, Japan and China, among other countries, for the first-line treatment of appropriate patients with metastatic nonsquamous non-small cell lung cancer."

Merck shares were marked modestly higher at $83.19 each, a move that would extend the stock's year-to-date gain to around 10%.

Keytruda sales were a big component of Merck's stronger-than-expected fourth quarter fourth quarter earnings, as well as its robust profit guidance for 2019, which the company posted earlier this month.

Merck said non-GAAP earnings for the three months ending in December came in at $1.04 per share, up 6.1% from the same period last year and one penny ahead of the consensus Street forecast.

Group sales, Merck said, rose 5% to $11 billion, just ahead of the $10.97 billion estimate, while Keytruda revenues rose 64% from last year to $2.15 billion, again beating the consensus forecast of $2.12 billion. For the whole of 2018, Keytruda sales rose 88% to $7.171 billion and comprised nearly a firth of Merck's entire topline.