To investigate the clinicopathologic characteristics and the impact of mismatch repair-deficient/microsatellite instability-high (MMRd/MSI-H) on oncologic outcomes of patients with endometrial cancer.
In this single-center, retrospective study, patients with endometrial cancer who underwent immunohistochemistry staining for MMR proteins (MLH1/MSH2/MSH6/PMS2) and/or next-generation sequencing for MSI status and genomic alterations between January 2011 and June 2021 were included. Data collected included patient demographics, clinicopathologic characteristics, treatment, and clinical outcomes.
Of the total 234 eligible patients, 182 patients (77.8%) had MMRp/non-MSI-H tumors and 52 patients (22.2%) had MMRd/MSI-H tumors. Between two groups, clinicopathologic characteristics including histologic type, grade, myometrial invasion, LVSI, LN metastasis were not statistically different. A total of 74 out of 234 patients were tested for PD-L1, and PD-L1 expression was observed in 52.6% in the MMRp/non-MSI-H group and 88.2% in the MMRd/MSI-H group (p=0.028). There was no statistically significant difference in recurrence rates and survival outcomes in relation to MMRd/MSI-H status (p=0.244 and 0.240, respectively). Among MMRd/MSI-H patients, six patients were treated with immune checkpoint inhibitors and objective response rate was 50.0%, comprised of 3 partial responses. A grade 3 or higher adverse event occurred in one patient, thrombocytopenia.
In patients with endometrial cancer, MMRd/MSI-H is not associated with oncologic outcomes. In clinical practice, immunotherapy was safe and efficacious in MMRd/MSI-H recurrent endometrial cancer.