Bristol-Myers Squibb’s new strategy In lung cancer relies on showing its new biomarker can help predict who benefits most from immunotherapy combinations. And Monday at the American Society of Clinical Oncology annual meeting, it rolled out data to support that notion.

Some doctors aren’t convinced, though—and they may just end up reaching for archnemesis Merck’s immuno-oncology star instead.

As part of the Checkmate-227 study, BMS segmented a group of patients whose tumors don’t bear the well-established biomarker PD-L1 to show that combinations featuring its PD-1 med Opdivo—Opdivo and fellow Bristol immunotherapy Yervoy, and Opdivo-plus-chemo—worked better in those with high levels of tumor mutational burden, or TMB.

The way BMS’ oncology development head, Fouad Namouni, sees it, "these data will be extremely important in understanding what population of patients is benefitting from I-O combination, whether it’s chemo combination or IO-IO," he said.

For one, they’ll save patients with low TMB and low PD-L1 levels—who "don’t seem to derive benefit from either a chemo combination or an IO combination" that other groups do—some unnecessary exposure to drugs that won’t work, and the side effects that go along with them. "For this reason, I really believe in studying a patients’ biomarker at the time of making treatment decisions," Namouni said.

Not everyone’s convinced that TMB should be included in the group of biomarkers that doctors routinely test for in newly diagnosed lung cancer patients. At an ASCO educational panel on Friday, presenting doctors "were all in agreement that TMB testing is not ready for routine clinical practice, recommending against testing all patients for it at this time," Credit Suisse analyst Vamil Divan wrote in a note to clients.

That discussion picked up right where it left off at April’s American Association for Cancer Research annual meeting, where Bristol worked to build its biomarker case with different Opdivo-Yervoy data in TMB-high patients.

The New Jersey drugmaker, naturally, feels differently about TMB testing; Namouni has said TMB could one day join EGFR, ALK, ROS and others on the list of lung cancer biomarkers used routinely to determine which treatments will work best.

In the meantime, though, Bristol’s chief I-O rival Merck is putting up big numbers across the board in the all-important first-line setting. Its combo of Keytruda and chemo has already shown it could halve the risk of death for patients with non-squamous lung cancer, and over the weekend at ASCO, the Keytruda-chemo pairing showed it could slash that risk by 36% in the squamous population, too.

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