(Reuters) -- Recent clinical trial results are likely to lead doctors to treat more patients who have a common form of lung cancer with a Merck drug at the expense of a Bristol-Myers Squibb medication at least until more data emerges, oncologists and analysts say.
The yet-to-be-published studies involve drugs in a new class designed to enable the body's immune system to fight cancer.
A recent trial of Merck's Keytruda (pembrolizumab) showed that it worked better than chemotherapy as an initial treatment for advanced non-small cell lung cancer (NSCLC) in patients with high levels of the PDL1 protein, believed to help identify those most likely to benefit from this type of immunotherapy.
A separate trial of Bristol-Myers' Opdivo (nivolumab), which included patients with much lower levels of the protein biomarker, did not show an advantage over chemotherapy.
"It seems likely that PDL1, if these results hold, will be added to the list of markers that someone needs prior to starting treatment," said Edward Garon, a lung cancer specialist at the University of California Los Angeles' Jonsson Comprehensive Cancer Center.
He said patients shown to have high levels of PDL1 will be started on the Merck drug, while those who test negative may continue to be treated with Opdivo.
Since Opdivo received regulatory approval for use without requiring patients to be tested for PDL1 and clinicians were unfamiliar with testing for the protein, doctors had favored use of the Bristol drug, Garon said.
That preference has played out in sales. Opdivo's second-quarter sales were $840 million, more than double those of Keytruda. Both drugs have U.S. prices of nearly $150,000 a year.
"I do think that more oncologists may start choosing Keytruda," Trevor Bivona, assistant professor of medicine and member of the University of California San Francisco's Helen Diller Family Comprehensive Cancer Center, said in an emailed statement.
Both drugs were approved by U.S. regulators last year for previously treated patients with advanced non-small cell lung cancer (NSCLC), the most common form of the disease, but have not yet been approved as initial lung cancer treatments.
Barbara Gitlitz, a lung cancer specialist and associate professor of clinical medicine at the University of Southern California, said she would now choose Keytruda for advanced lung cancer patients with high levels of PDL1 who were not in a clinical trial.
A survey of 79 U.S. and European oncologists, published last week by investment services firm AllianceBernstein, found that 57% of respondents anticipated using more Keytruda as a result of the latest trial results, and 70% said they will be more likely to order PDL1 testing for patients.
Bristol-Myers earlier this month said its trial failed to show that Opdivo worked better than chemotherapy for previously untreated patients with advanced NSCLC. The trial included patients with tumors testing 5% or higher for PDL1.
In June, Merck said trial data showed that Keytruda worked better than chemo as an initial treatment for advanced NSCLC patients with PDL1 levels of at least 50%.
The Merck and Bristol-Myers trial results were summarized in press releases but complete results have not been presented.
Full results could include a breakdown of how Opdivo fared in patients with high levels of PDL1, but investors have already shifted their bets. Shares of Bristol-Myers have fallen more than 20% since the latest trial results were announced, while shares of Merck rose nearly 10% over the same period.
Besides Bristol and Merck, companies including Roche Holding AG and AstraZeneca PLC are developing immune-system boosting drugs for treating lung cancer. Clinicians and investors are awaiting more trial data, including a range of studies examining combinations of these drugs.
Lung cancer, the leading cause of cancer deaths worldwide, kills an estimated 1.6 million people each year, according to the World Health Organization.