Real‑World Treatment Patterns in Endometrial Cancer in the Post-Immune Checkpoint Inhibitor and Post-Platinum-Based Chemotherapy Setting in the United States

Immune checkpoint inhibitors (ICI), either following or in combination with platinum chemotherapy (PT), are routinely used to treat endometrial cancer (EC). Subsequently, a post-ICI and post-PT patient population is emerging with no approved therapy or guideline-recommended treatment approach for this setting. As novel therapies are being explored, it is critical to understand the patient characteristics and real-world treatment patterns in this setting. This retrospective observational study used de-identified electronic health record data from the Flatiron Health database (2013–2026). Adult women with EC who had prior exposure to both ICI and PT and subsequently initiated a new regimen (the index line of therapy [LOT]) were included. The results were stratified by mismatch repair and microsatellite instability (MMR/MSI) status, and treatment patterns were summarized descriptively. A total of 564 women met the selection criteria, including 34 (6.0%) treated in the first LOT, 188 (33.3%) in the second LOT, 189 (33.5%) in the third LOT, and 153 (27.1%) in the fourth LOT or later. Among patients with deficient MMR/MSI-High (dMMR/MSI-H) tumors, post-ICI and post-PT regimens usually included hormonal therapy (18.0%) and ICI monotherapy (14.0%). Among patients with proficient MMR and microsatellite stable (pMMR/MSS) tumors, chemotherapy monotherapy (25.7%) and ICI plus tyrosine kinase inhibitor combinations (11.9%) were most frequent. A total of 228 patients (40.4%) received an ICI-containing regimen at the index LOT or a subsequent line, of whom 179 (78.5%) received a pembrolizumab-containing regimen, 21 (9.2%) a dostarlimab-containing regimen, and 28 (12.3%) other ICI-containing regimens. In EC, the post-ICI and post-PT patient population is growing, particularly in the second LOT and earlier settings. Treatment following ICI and PT exposure in EC was highly variable, with no dominant regimen identified regardless of MMR/MSI status.