(Adds company, analyst comments, updates shares)
By Manas Mishra and Manojna Maddipatla
Feb 1 (Reuters) - Merck & Co's cancer immumotherapy Keytruda compiled sales that topped $2 billion in a quarter for the first time, exceeding Wall Street's lofty estimates and sending shares up more that 3 percent on Friday.
Keytruda has been Merck's most important growth driver with its domination of the lucrative lung cancer space, and shows no sign of slowing as it produces positive clinical data and adds approvals for different types of cancer.
"The key to the Merck story remains continued strong commercial uptake of Keytruda and the release of additional positive clinical data," Credit Suisse analyst Vamil Divan said.
The company also reported slightly higher-than-expected fourth-quarter profit as Keytruda sales jumped 66 percent to $2.15 billion, compared with analysts' estimate of $2.12 billion, according to IBES data from Refinitiv.
Keytruda has become the drug of choice as an initial, or first-line, treatment of advanced lung cancer, helping it to widen the gap with Bristol-Myers Squibb Co's rival drug Opdivo, which had been the early leader among treatments that help the immune system attack tumors. Opdivo had fourth-quarter sales of $1.8 billion.
Merck's Gardasil vaccine to prevent certain types of cancer also had a good quarter with sales up 32 percent to $835 million.
The company issued a 2019 earnings forecast with a midpoint a bit below Wall Street estimates, following a trend seen this month among other large drugmakers, including Johnson & Johnson , Pfizer Inc, Bristol-Myers and Amgen Inc . But with a focus squarely on Keytruda sales, that did little to dampen investor enthusiasm.
Merck shares were up 3.5 percent at $77.05.
The New Jersey-based drugmaker forecast 2019 adjusted earnings of $4.57 to $4.72 per share versus analysts' estimate of $4.68. It forecast full-year revenue of $43.2 billion to $44.7 billion, compared with analysts' estimate of $44.53 billion.
Merck's Zostavax vaccine to prevent shingles continued to lose significant ground to GSK's rival Shingrix, with sales falling by more than half to $54 million.
Sales of the related diabetes treatments Januvia and Janumet dipped 4 percent amid increasing competition to $1.47 billion.
Excluding items, Merck earned $1.04 per share, beating analysts' average expectations by a penny.
Merck said it was not in the market for "mega-mergers" such as Bristol's planned $74 billion purchase of Celgene Corp .
"We want to focus on the kind of deals that we can add with a minimum of disruption to our ongoing scientific efforts," Chief Executive Kenneth Frazier said. (Reporting by Manas Mishra and Manogna Maddipatla in Bengaluru; Editing by Shinjini Ganguli and Bill Berkrot)