Outcomes following complete response to immune checkpoint inhibitors in endometrial cancer

OBJECTIVES: Immune checkpoint inhibitors have transformed treatment for advanced and recurrent endometrial cancer (EC), yet optimal management after complete response (CR) remains unclear. We evaluated clinical outcomes and durability of response among patients with mismatch repair deficient (MMRd) and proficient (MMRp) EC who achieved CR following PD-1/PD-L1-directed immunotherapy. METHODS: We performed a retrospective single-institution study of patients with EC who achieved a CR to immunotherapy between June 2016 and November 2025. Clinical characteristics, treatment details, and outcomes were abstracted from medical records. Time-to-event outcomes were estimated using Kaplan-Meier methods. RESULTS: Among 192 patients with EC treated with immunotherapy, 57 (29.7%) achieved a CR, including 37 (64.9%) with MMRd and 20 (35.1%) with MMRp tumors. Most (67%) received treatment for recurrent disease. Median time to CR was 7.2 months. At a median follow-up of 53.5 months for MMRd and 21.4 months for MMRp disease, 37 patients (64.9%) remained alive and disease-free, 86.5% of whom were off treatment. Among patients with recurrent disease who discontinued immunotherapy for reasons other than progression or death (n = 30), 27 (90%) remained recurrence-free, including five who later died of unrelated causes. Three patients (10%) experienced recurrence after discontinuation. CONCLUSIONS: In this retrospective analysis, CRs to immunotherapy were observed in both MMRd and MMRp EC, with a trend toward greater durability in MMRd tumors. Most patients who achieved CR remained disease-free at last follow-up, including many with recurrent disease who maintained remission for at least two years after treatment discontinuation, supporting the durability of response.