FDA Approves FoundationOne CDx to Identify MSI-High Cancers for Pembrolizumab Therapy


The FDA designated the FoundationOne CDx assay as a companion diagnostic for identifying tumors that are microsatellite instability–high and may benefit from pembrolizumab.

The FDA has announced approval of FoundationOne CDx as a companion diagnostic for identifying people with microsatellite instability (MSI)–high cancers who may be candidates for treatment with pembrolizumab (Keytruda), according to a press release from the assay developer Foundation Medicine, Inc.1

The decision from the agency makes the assay the only approved companion diagnostic for this indication.

“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,” Mia Levy, MD, PhD, chief medical officer at Foundation Medicine, said in a press release. “Not only could this approval allow more patients to benefit from Keytruda, but it also underscores an important shift toward tumor-agnostic cancer care.”

Pembrolizumab was granted accelerated approval in the treatment of adult and pediatric patients with unresectable or metastatic, MSI-high or mismatch repair deficient solid tumors after disease progression on prior therapies and for whom there are no satisfactory alternatives based on the data from 5 multi-cohort, single-arm clinical trials.2

The FoundationOne CDx uses formalin-fixed, paraffin-embedded tumor tissue specimens to detect gene mutations and alterations, as well as genomic signatures like MSI and tumor mutational burden by way of next-generation sequencing based on in vitro diagnostics.

Previously, the assay received approval as a companion diagnostic across various indications, such as osimertinib (Tagrisso) for non­–small cell lung cancer with EGFR exon 19 deletions or EGFR exon 21 L858R alterations, trastuzumab (Herceptin) for HER2-positive breast cancer, pemigatinib for cholangiocarcinoma harboring FGFR2 fusions or rearrangements, and larotrectinib (Vitrakvi) for patients with NTRK1/2/3 fusion–positive solid tumors.3 The current approval marks the twenty-sixth unique companion diagnostic indication that span 27 targeted therapies.

“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,” Eric Rubin, senior vice president of early-stage development, clinical oncology at Merck Research Laboratories, said in a statement.


  1. U.S. FDA approves foundationOne CDx as a companion diagnostic for Keytruda (pembrolizumab) to identify patients with microsatellite instability-high (MSI-H) solid tumors. News release. Foundation Medicine, Inc. February 21, 2022. Accessed February 21, 2022. https://bit.ly/3JERVLq
  2. FDA grants accelerated approval to pembrolizumab for first tissue/site agnostic indication. News release FDA. May 23, 2017. Accessed February 21, 2022. https://bit.ly/3H6KqeB
  3. List of cleared or approved companion diagnostic devices (in vitro and imaging tools). News release. FDA. December 1, 2021. Accessed February 21, 2022. https://bit.ly/3h0FD3R
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