The economic value of mismatch repair-guided immunotherapy in endometrial cancer: companion testing and patient selection.

Mismatch repair (MMR) status has moved from hereditary-cancer screening to a central predictive biomarker for immunotherapy in endometrial cancer. The marked difference in treatment benefit between MMR-deficient/microsatellite instability-high (dMMR/MSI-H) and MMR-proficient/microsatellite-stable (pMMR/MSS) tumors creates an economic rationale for companion testing, but the value of testing depends on assay accuracy, treatment price, duration, survival extrapolation, and local willingness-to-pay thresholds. This Mini Review examines the clinical and economic value of MMR-guided immunotherapy in advanced and recurrent endometrial cancer. A targeted literature search of PubMed/MEDLINE, Embase, Web of Science, and the Cochrane Library from database inception through 31 July 2026. We summarize practical testing pathways based on four-protein immunohistochemistry, reflex mutL homolog 1 (MLH1) promoter methylation, MSI assays, and selective next-generation sequencing; review MMR-stratified evidence from major immunotherapy trials; and compare published cost-effectiveness analyses of pembrolizumab, dostarlimab, atezolizumab, durvalumab-based regimens, and pembrolizumab plus lenvatinib. Across studies, dMMR/MSI-H disease generally generates the largest quality-adjusted survival gains and the most favorable incremental cost-effectiveness ratios, whereas the economic case in pMMR/MSS disease is more sensitive to drug pricing and modeling assumptions. Overall, MMR testing can function as an allocation technology that prioritizes high-value treatment, while future work should harmonize testing, manage discordant results, refine biomarkers for pMMR tumors, and incorporate long-term survival, quality of life, equity, and value of information into economic models.