Microsatellite Instability Test Gains FDA Approval for Immunotherapy Selection

Microsatellite instability-high (MSI-H) status is a key tumor biomarker used to guide treatment decisions in precision oncology. Testing can identify adult and pediatric patients with unresectable or metastatic MSI-H or mismatch repair-deficient cancers who have progressed after prior treatment and lack satisfactory alternatives. A newly approved PCR-based companion diagnostic supports these decisions by identifying MSI-H solid tumors in patients who may be eligible for KEYTRUDA therapy.

The Promega (Madison, WI, USA) OncoMate MSI Dx Analysis System has received U.S. Food and Drug Administration (FDA) approval as a companion diagnostic for KEYTRUDA (pembrolizumab), Merck’s anti-PD-1 therapy, in patients with microsatellite instability-high (MSI-H) solid tumors. The approval enables the PCR-based assay to help identify patients who may benefit from KEYTRUDA treatment. Merck markets the therapy under its own name in the United States and Canada and as MSD elsewhere.

The OncoMate MSI Dx Analysis System evaluates microsatellite instability status in solid tumor tissue to support treatment selection and precision oncology strategies. The latest approval, supported through a collaboration with Merck, expands the system’s role in identifying patients who may benefit from targeted immunotherapy.

The system previously received FDA clearance as the first PCR-based molecular diagnostic to identify colorectal cancer patients who may benefit from further testing for Lynch syndrome. It is also approved as a companion diagnostic for identifying patients with microsatellite-stable (MSS) endometrial carcinoma who may benefit from KEYTRUDA plus LENVIMA (lenvatinib), a multiple receptor tyrosine kinase inhibitor discovered by Eisai. 

These U.S. authorizations complement international regulatory milestones, including CE marking under the European Union’s In Vitro Diagnostic Regulation (IVDR) and approval by China’s National Medical Products Administration (NMPA) as a companion diagnostic for KEYTRUDA in MSI-H solid tumors.

“This approval reflects our dedication to providing meaningful diagnostic advances, developed to the highest quality and regulatory standards. Our test connects patients with the therapy most likely to help them, working alongside our pharmaceutical collaborators and the clinicians who use the result,” said Alok Sharma, Global Clinical Market Director at Promega.

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