IHC Companion Diagnostic Standardizes Mismatch Repair Testing for Cancer Immunotherapy

Deficient DNA mismatch repair is an established predictive biomarker for response to immune checkpoint inhibitors, yet access to standardized assessment has varied across tumor types. Cancer remains the second leading cause of death worldwide, underscoring the need to align testing with therapies across solid tumors. A newly IVDR‑approved immunohistochemistry test now standardizes mismatch repair evaluation to help identify patients eligible for several precision oncology regimens.

Roche’s VENTANA MMR RxDx Panel is an immunohistochemistry (IHC) companion diagnostic designed to determine a patient’s mismatch repair (MMR) status by evaluating MMR proteins in tumor tissue. Positioned as a first-of-its-kind panel, its latest European Union In Vitro Diagnostic Regulation (IVDR) decision expands the on-market label. The test is now available in IVDR-regulated countries as a companion diagnostic across five cancer types and six indications.

The assay measures expression of MMR proteins in formalin‑fixed, paraffin‑embedded (FFPE) tumor sections using the OptiView DAB IHC Detection Kit. It incorporates VENTANA anti‑MLH1 (M1), anti‑MSH2 (G219‑1129), and anti‑MSH6 (SP93) antibodies with OptiView DAB IHC Detection, and VENTANA anti‑PMS2 (A16‑4) with OptiView Amplification, on the BenchMark ULTRA instrument. By assessing loss of expression across these proteins, the panel provides a standardized approach to classifying MMR deficiency in solid tumors.

With this IVDR approval, the panel serves as a companion diagnostic for multiple therapies and indications. It supports KEYTRUDA (pembrolizumab) for mismatch repair–deficient (dMMR) tumors in certain adults with metastatic colorectal cancer; advanced or recurrent endometrial carcinoma; and unresectable or metastatic gastric, small intestine, or biliary cancer. It is also a companion diagnostic for IMFINZI (durvalumab) in adult patients with dMMR primary advanced or recurrent endometrial cancer, and for JEMPERLI (dostarlimab-gxly) in dMMR endometrial cancer.

In addition, the panel supports IMFINZI plus LYNPARZA (olaparib) in adult patients with mismatch repair–proficient (pMMR) primary advanced or recurrent endometrial cancer. The label expansion builds on evidence that MMR proteins are predictive biomarkers for PD-1–targeted therapy and that dMMR tumors may respond well to PD-1 or PD-L1 inhibitors. For pMMR endometrial cancer, combining a poly(ADP-ribose) polymerase (PARP) inhibitor with an immune checkpoint inhibitor may enhance clinical benefit.

“By providing a standardised testing option for mismatch repair status with our VENTANA MMR RxDx Panel, we are empowering clinicians to make more informed decisions and expanding access to important therapies for patients across multiple solid tumor types,” said Laura Apitz, Head of Pathology Lab at Roche Diagnostics. “This milestone exemplifies our dedication to delivering high-medical-value solutions that help improve patient outcomes through precision medicine.”