FDA Approves OncoMate MSI Dx as Pembrolizumab Companion Diagnostic in MSI-H Solid Tumors

The FDA has approved the OncoMate MSI Dx Analysis System as a companion diagnostic for pembrolizumab (Keytruda) in patients with microsatellite instability–high (MSI-H) solid tumors, according to a news release from the developer, Promega.¹

The OncoMate MSI Dx Analysis System is a PCR-based assay that evaluates microsatellite instability (MSI) status in solid tumor tissue. According to the release, MSI status can inform treatment decisions and support precision oncology. The US approvals for the system apply to the United States and its territories.

“This approval reflects our dedication to providing meaningful diagnostic advances, developed to the highest quality and regulatory standards,” said Alok Sharma, global clinical market director at Promega, in the press release.¹ “Our test connects patients with the therapy most likely to help them, working alongside our pharmaceutical collaborators and the clinicians who use the result.”

What is the regulatory history of the OncoMate MSI Dx system?

The OncoMate MSI Dx system was previously cleared by the FDA as the first PCR-based molecular diagnostic to identify patients with colorectal cancer who may benefit from additional testing for Lynch syndrome. It is also an approved companion diagnostic for identifying patients with microsatellite-stable endometrial carcinoma who may benefit from pembrolizumab plus lenvatinib (Lenvima).²

That combination was evaluated in the phase 3 KEYNOTE-775 trial (NCT03517449) of 827 patients with previously treated advanced endometrial cancer. In the updated analysis (data cutoff, March 2022), the median overall survival in the mismatch repair–proficient (pMMR) population was 18.0 vs 12.2 months with physician's choice chemotherapy (HR, 0.70; 95% CI, 0.58-0.83). The median progression-free survival was 6.7 vs 3.8 months (HR, 0.60; 95% CI, 0.50-0.72), and the objective response rate (ORR) was 32.4% vs 15.1%.³

Outside the United States, the technology is CE-marked under the European Union's In Vitro Diagnostic Regulation, and China's National Medical Products Administration has approved it as a companion diagnostic for pembrolizumab in MSI-H solid tumors.¹

What is the pembrolizumab indication in MSI-H solid tumors?

Pembrolizumab is indicated for adult and pediatric patients with unresectable or metastatic MSI-H or mismatch repair–deficient (dMMR) solid tumors, as determined by an FDA-approved test, who have progressed following prior treatment and who have no satisfactory alternative treatment options.⁴ Merck announced on March 29, 2023, that the FDA had converted the indication, which received accelerated approval in 2017, to a full approval.⁴

The conversion was supported by 504 adult and pediatric patients in the phase 2 KEYNOTE-158 (NCT02628067), KEYNOTE-164 (NCT02460198), and KEYNOTE-051 (NCT02332668) trials. The pooled ORR was 33.3% (95% CI, 29.2%-37.6%), including a complete response rate of 10.3% and a partial response rate of 23.0%, at a median follow-up of 20.1 months. The ORR was 34% (95% CI, 26%-43%) in 124 patients with colorectal cancer and 33% (95% CI, 28%-38%) in 380 patients with noncolorectal tumors.

Among 168 responders, 77% had responses lasting at least 12 months and 39% had responses lasting at least 36 months. The median duration of response was 63.2 months (range, 1.9+ to 63.9+).

References

1. FDA approves Promega OncoMate MSI Dx Analysis System as companion diagnostic for KEYTRUDA in MSI-high solid tumors. News release. Promega Corporation. November 9, 2026. Accessed November 10, 2026. https://tinyurl.com/yd5tr8jt
2. FDA approves Promega OncoMate MSI Dx Analysis System as companion diagnostic for KEYTRUDA in combination with LENVIMA in advanced endometrial carcinoma. News release. Promega. November 11, 2025. Accessed November 10, 2026. https://tinyurl.com/2jdnn7r7
3. Makker V, Colombo N, Casado Herráez A, et al. Lenvatinib plus pembrolizumab in previously treated advanced endometrial cancer: updated efficacy and safety from the randomized phase III study 309/KEYNOTE-775. J Clin Oncol. 2023;41(16):2904-2910. doi:10.1200/JCO.22.02152
4. FDA converts to full approval indication for KEYTRUDA (pembrolizumab) for certain adult and pediatric patients with advanced microsatellite instability-high (MSI-H) or mismatch repair deficient (dMMR) solid tumors. News release. Merck. March 29, 2023. Accessed November 10, 2026. https://bit.ly/40rC1N4