Cancer cells, illustration
Credit: JESPER KLAUSEN / SCIENCE PHOTO LIBRARY/Getty Images

The first test for Microsatellite Instability High (MSI-H) status in solid tumors has been approved by the U.S. Food and Drug Administration (FDA), according a release from Foundation Medicine. FoundationOne CDx is the only FDA-approved companion diagnostic to help identify patients with MSI-H solid tumors, which may be appropriate for treatment with Merck’s anti-PD-1 therapy, Keytruda (pembrolizumab).

In tumors that are defined as MSI-H, the DNA repair mechanisms are faulty. As a result, tumor cells can acquire a significant number of mutations that can make them recognizable by the immune system.

“Immunotherapy has huge promise as a potential treatment option for patients with advanced cancer; however, identifying those who may benefit is complex and requires high-quality diagnostics,” said Mia Levy, chief medical officer at Foundation Medicine. “Not only could this approval allow more patients to benefit from Keytruda but it also underscores an important shift toward tumor-agnostic cancer care.”

MSI-H status is more commonly found in colorectal, endometrial, and gastrointestinal cancers, but it can also be seen in other types of cancer. Keytruda was granted accelerated approval to treat certain patients with MSI-H solid tumors in May 2017, making it the first targeted therapy approved to treat patients based on a genomic signature, instead of where the tumor originated in the body.

In June 2020, this test was the first approved to identify patients with TMB-H solid tumors who may benefit from treatment with Keytruda, which was approved under accelerated approval for the treatment of adult and pediatric patients with unresectable or metastatic tumor mutational burden-high (TMB-H) [≥10 mutations/megabase (mut/Mb)] solid tumors, as determined by an FDA-approved test. TMB is a measure of the number of somatic mutations per coding region within a tumor’s genome.

This MSI-H approval is the third tumor agnostic companion diagnostic nod for FoundationOne CDx. In October 2020, FoundationOne CDx was approved as to guide the use of Fitrakis (larotrectinib), which is approved for the treatment of adult and pediatric patients with solid tumors that have a neurotrophic receptor tyrosine kinase (NTRK) gene fusion.

The company now has 26 companion diagnostic claims and two group claims across 27 targeted therapies. These include approvals as a companion diagnostic with Tagrisso (osimertinib) for non­–small cell lung cancer certain EGFR deletions and alterations, Herceptin (trastuzumab) for HER2-positive breast cancer, and Pemazyre (pemigatinib) for cholangiocarcinoma harboring FGFR2 fusions or rearrangements.

“We’re proud to see this collaboration with Foundation Medicine, which drew on the deep scientific expertise of both organizations, result in another companion diagnostic approval for use in identifying patients who may be appropriate for KEYTRUDA,” said Eric Rubin, senior vice president, early-stage development, clinical oncology, Merck Research Laboratories.

Foundation reports that it has more than 65 biopharma partners. Earlier this month, they announced a collaboration with Eli Lilly and Company (Lilly) for the development of Foundation Medicine’s tissue- and blood-based assays as companion diagnostics for RETEVM and other therapies in Loxo Oncology at Lilly’s pipeline. That partnership will initially explore the use of FoundationOne CDx for adult patients with metastatic rearranged transfection (RET) fusion across tumor types who may be eligible for Lilly’s RET inhibitor, RETEVMO in the United States and European Union.

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