Prognostic impact of mismatch repair deficiency in high- and low-intermediate-risk, early-stage endometrial cancer following vaginal brachytherapy

To examine the impact of mismatch repair (MMR) status on prognosis among patients with high- and low-intermediate-risk endometrioid endometrial cancer (EEC) treated with vaginal brachytherapy (VBT).198 stage I-II EEC patients with known MMR status treated with adjuvant VBT were identified. Both low-intermediate (LIR) and high-intermediate-risk (HIR) patients were included. Clinical characteristics were compared between patients with proficient and deficient mismatch repair (pMMR and dMMR) using Fisher's exact tests for categorical variables and t-tests for continuous variables. Recurrence-free survival (RFS) and overall survival (OS) were analyzed with Kaplan-Meier estimates, the log-rank test, and Cox proportional hazards regression.Patients with dMMR compared to pMMR were more likely to have grade 2-3 tumors (75% vs. 57%, p = 0.006), lympho-vascular invasion (40% vs. 25%, p = 0.034), and HIR classification (65% vs. 49%, p = 0.011). Three-year RFS was inferior for dMMR compared to pMMR patients (75% vs. 96%, p = 0.001). dMMR patients compared to pMMR had similarly reduced 3-year RFS within the LIR (74% vs. 100%, p = 0.026) and HIR (75% vs. 91%, p = 0.038) subgroups. Three-year OS was not different between dMMR/pMMR patients (98% vs. 97%, p = 0.653) or HIR/LIR patients (97% vs. 97%, p = 0.999). On multivariable Cox regression, dMMR status was a significant prognostic variable for RFS (HR 3.774, CI 1.495-9.526, p = 0.005), though it was not significant for OS.Following VBT, patients with dMMR have poorer RFS compared to pMMR patients regardless of HIR/LIR risk classification. The prognosis of intermediate-risk EEC patients may lie more on a continuum dependent on molecular features rather than distinct clinicopathologic risk categories.