Introduction Dostarlimab, a programmed death 1 inhibitor, is approved in Korea for patients with mismatch repair deficient/microsatellite instability-high (dMMR/MSI-H) recurrent or advanced endometrial cancer (EC) that has progressed on or after treatment with a platinum-based chemotherapy. Through the Korean expanded access program (EAP), patients at 16 major medical institutions were able to access dostarlimab treatment. For the first time, we present real-world data from these Korean patients.

Methods Patients with recurrent/advanced dMMR/MSI-H EC with ≤2 lines of prior systemic chemotherapy and no prior anti-PD-(L)1 agent received 500 mg of dostarlimab intravenously once every 3 weeks for 4 cycles, then 1000 mg once every 6 weeks until disease progression or withdrawal from treatment. Tumor response and adverse events were recorded.

Results At data cutoff of August 1, 2023, 17 patients were accepted into the EAP. Median age was 57 years (range, 42–71 years). With a median follow-up of 3.75 months, 10 patients were available for evaluation of tumor response. Of these, 6 had confirmed complete or partial responses; objective response rate was 60.0%. Treatment-related adverse events (TRAEs) were experienced by 5.9% (1/17) of patients, with no grade ≥3 TRAEs. No patients discontinued because of TRAEs.

Conclusion/Implications Initial results from the Korean EAP of dostarlimab monotherapy treatment for patients with recurrent or advanced dMMR/MSI-H EC demonstrated encouraging antitumor activity with no new safety signals, further supporting dostarlimab use in Korean patients. Results were consistent with the GARNET clinical trial (NCT02715284) of dostarlimab monotherapy. Additional follow-up is ongoing.