Impact of metastatic sites on response to immunotherapy in patients with advanced or recurrent endometrial cancer.

e17632 Background: Patients with advanced or recurrent endometrial cancer have a median progression-free survival (PFS) of 3-6 months and a 5-year survival rate of 17%, with limited therapeutic options. Recent studies indicate combination of chemotherapy and immunotherapy significantly increased PFS among patients with primary advanced or recurrent endometrial cancer, with a substantial benefit in mismatch repair-deficient (dMMR), microsatellite instability-high (MSI-H) population. Prior studies have shown reduced response to immunotherapy across different metastatic sites in various solid tumors, such as melanoma, colorectal and non-small cell lung cancer. This study explores the impact of metastatic sites on treatment outcomes in patients with advanced or recurrent endometrial cancer. Methods: In this single-center retrospective study of patients diagnosed with metastatic or recurrent endometrial cancer who received IO between 10/2019 and 12/2024, demographic characteristics, therapy received, site of metastatic disease (lung, liver, lymph node, brain), response to treatment were obtained from the medical records. Response was defined as partial or complete response and no response was defined as progression or stable disease. The association between site of metastatic disease and response was assessed using Fisher’s Exact Test. Results: We identified 21 patients with metastatic or recurrent endometrial cancer who received IO at MD Anderson Cancer Center. The majority identified as White (67%, n = 14) and Not Hispanic (60%, n = 12) with a median age of 68 (IQR: 61-71). Histologies include endometrioid (62%, n = 13), serous (33%, n = 7), clear cell (19%, n = 4) with 3 patients demonstrating multiple histologies. Patients received pembrolizumab and lenvatinib (67%, n = 14, median number of cycles 5.5) and pembrolizumab monotherapy (33%, n = 7, median number of cycles 9). The overall response to IO was stable disease (5%, n = 1), progression (38%, n = 8), partial response (38%, n = 8), and complete response (19%, n = 4). Patients received pembrolizumab and lenvatinib (67%, n = 14, median number of cycles 5.5) and pembrolizumab monotherapy (33%, n = 7, median number of cycles 9). The overall response to IO was stable disease (5%, n = 1), progression (38%, n = 8), partial response (38%, n = 8), and complete response (19%, n = 4). The odds ratios (OR) for overall response based on site of metastatic disease were liver (OR 1.77, p= 0.62), lung (OR 0.86, p= 1), lymph node (OR 1.04, p= 1), and bowel (OR not reported). Conclusions: This descriptive analysis identified patients with recurrent or advanced endometrial cancer with liver, lung, lymph node, and bowel metastases who received IO. Further retrospective data collection is underway to identify a possible role for site of disease, molecular signature, and response to IO.