(Adds stock moves, analyst comment)
By Bill Berkrot
April 16 (Reuters) - Merck & Co's immunotherapy Keytruda plus chemotherapy significantly improved overall survival in newly-diagnosed patients with advanced non-small cell lung cancer in a closely-watched study, cementing its lead position over Bristol-Myers Squibb Co and others in the most lucrative oncology market.
The survival data sent Merck shares up 2.4 percent to $58.55, while shares of Bristol-Myers plunged 8 percent to $53.93 despite positive lung cancer data for its immunotherapy combination in a subset of patients with a high degree of tumor mutations.
"Merck appears to be the clear winner so far," Credit Suisse analyst Vamil Divan said in a research note. He said the Merck data was better than expected across all patient subgroups, while questions remain about Bristol's Opdivo and Yervoy combination "until we see full data."
The magnitude of the survival benefit in the late-stage study was not yet known, but Keytruda plus chemotherapy cut the risk of death by 51 percent compared with chemotherapy alone, according to data presented at the American Association of Cancer Research meeting in Chicago on Monday.
"We don't know how long their survival is going to be and we're excited about that," said Dr. Leena Gandhi, the study's primary investigator, who called the results "practice changing."
Bristol-Myers's combination therapy significantly stalled disease progression versus standard chemotherapy in newly-diagnosed advanced non-small cell lung cancer (NSCLC) for patients with a high tumor mutational burden (TMB), a potentially important new biomarker for identifying those most likely to benefit from immunotherapy.
But overall survival is considered the gold standard by doctors and investors, giving Keytruda a clear leg up.
The Keytruda plus chemotherapy regimen was approved as an initial, or first-line, treatment for advanced NSCLC patients based on earlier data from a small study. But many clinicians wanted to see validation of a survival benefit in a large trial.
"We were all waiting to see a definitive Phase III study that showed very clear cut results," said Gandhi, director of thoracic medical oncology at NYU Langone in New York.
Keytruda and Opdivo have piled up approvals for advanced cancers, such as for melanoma and bladder cancer. But those drugs and rival immunotherapies from Roche and AstraZeneca are jockeying for pieces of the largest lung cancer market. Thus far, Merck has dominated the coveted newly-diagnosed setting.
There are more than 200,000 new cases of NSCLC each year in the United States alone, with about half at advanced stage at the time of initial diagnosis.
In the Merck-sponsored trial called Keynote-189, median overall survival was 11.3 months for chemotherapy, about what was expected. After 12 months, 69.2 percent of patients in the Keytruda group were alive compared with 49.4 percent for chemotherapy, researchers reported.
The differences would likely have been more pronounced, but many patients in the chemotherapy group were given Keytruda or a similar drug once their disease progressed.
In the study called CheckMate-227, 43 percent of patients with high TMB who received Opdivo and low-dose Yervoy experienced no disease progression after one year versus 13 percent in the chemotherapy group. There was preliminary evidence of a likely survival benefit but it was too early to determine that, researchers said.
The overall response rate - those with significant tumor shrinkage - was 45 percent for the immunotherapies versus 27 percent for chemotherapy.
Dr. Matthew Hellman of Memorial Sloan Kettering Cancer Center in New York, who led the study, said it was a validation of TMB as a biomarker and that Opdivo with Yervoy should be an important chemotherapy-sparing regimen in first-line lung cancer.
In both studies, the positive results were not dependent on cancer cell's levels of PD-L1, a marker of inflammation that has been commonly used with drugs like Keytruda and Opdivo to help predict patient responses, with higher PD-L1 levels believed to lead to greater efficacy.
"This is great that there's new options and improved outcomes" for patients with lung cancer, Hellman said of the two studies.
(Reporting by Bill Berkrot; editing by Diane Craft and Susan Thomas)