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Merck Nabs Full FDA Approval for Keytruda in MSI-High, dMMR Solid Tumors

NEW YORK – The US Food and Drug Administration on Thursday granted a full approval to Merck's PD-L1 checkpoint inhibitor Keytruda (pembrolizumab) as a treatment for advanced solid tumors with high microsatellite instability (MSI) or mismatch-repair deficiencies (dMMR).

The tumor-agnostic indication — the first of two for Keytruda — received accelerated approval from the FDA in 2017. Now, the agency has decided to convert the label to a full approval based on updated results from three Phase II clinical trials: KEYNOTE-158, KEYNOTE-164, and KEYNOTE-051.

Together, the trials include data from 504 patients across more than 30 tumor types whose cancers were MSI-high or dMMR according to testing with polymerase chain reaction or immunohistochemistry either locally or centrally performed.

In a pooled analysis of the three trials after a median follow-up time of 20.1 months, Keytruda resulted in a 33.3 percent overall response rate, a 10.3 percent complete response rate, and a 23 percent partial response rate. Of 168 patients whose tumors responded to Keytruda, 77 percent experienced responses lasting more than a year and 39 percent had responses lasting more than three years. The median duration of response was 63.2 months.

"This approval reinforces the important role of Keytruda in certain patients with MSI-H or dMMR solid tumors facing a variety of cancers," Luis Diaz, head of the solid tumor oncology division at Memorial Sloan Kettering Cancer Center, said in a statement. "These data also further underscore the need for biomarker testing to identify patients who may be eligible for this therapy."

The conversion marks the first time the FDA has granted full approval to an immunotherapy in a tumor-agnostic, biomarker-selected indication. Keytruda has another tumor-agnostic approval, however — this one still an accelerated approval — for patients with tumor mutational burden (TMB)-high cancers as determined by Foundation Medicine's next-generation sequencing test, FoundationOne CDx.