Molecular markers in recurrent stage I, grade 1 endometrioid endometrial cancers.

Objectives: Stage I, grade 1 endometrial cancers have low recurrence rates and often do not receive adjuvant therapy. We compared recurrent cases to matched non-recurrent controls to evaluate for molecular markers associated with higher risk of recurrence.

Methods: A case-control study including all cases of recurrent stage I, grade 1 endometrioid endometrial cancer at one institution in a ten-year period. Cases were matched to controls by age, BMI, weight and stage. Molecular testing and immunohistochemistry were performed on archival tumor specimens: microsatellite instability (MSI-H), mismatch repair status, POLE mutational status, and next-generation sequencing.

Results: 15 stage I, grade 1 endometrial cancer cases with recurrent disease and available tumor specimens were identified. CTNNB1 and MSI-H were present at significantly higher rates in cases than controls (CTNNB1 60% vs. 28%, OR 3.9, 95%CI 1.1-14.7, p = 0.04 and MSI-H 53% vs. 21%, OR 4.4, 95%CI 1.1-17.0, p = 0.03). POLE mutations were found in 0% of cases vs. 7% of controls (p = 0.54). Among specimens demonstrating microsatellite stability (MSS), 100% of cases vs. 26% of controls had CTNNB1 mutations (p < 0.001). CTNNB1 wild type tumors were MSI-H in 100% of cases vs. 19% of controls (p < 0.001).

Conclusions: Compared to controls, CTNNB1 mutation is present at significantly higher rates in recurrent stage I, grade 1 endometrial cancers and is found most commonly in MSS tumors. MSI-H is also present at significantly higher rates in recurrent cases. These markers may be useful for prognostic risk stratification and adjuvant therapy decision-making in this otherwise low-risk population.