Recurrent Distant Metastatic Endometrial Cancer Treated with Immunotherapy with Pembrolizumab: A Case Report and...

Background and Clinical Significance: Advanced-stage and recurrent metastatic endometrial cancer (EC) is a complex and challenging disease with a poor prognosis. Immunotherapy is a promising treatment for advanced and recurrent mismatch repair deficiency (MMRd) EC. Case Presentation: A 57-year-old female patient with stage 2 dedifferentiated EC with MMRd (immunohistochemistry revealed PMS2 loss) and stage 1 renal clear cell carcinoma received neoadjuvant chemotherapy, underwent radical hysterectomy, received adjuvant chemotherapy and radiotherapy, and underwent partial nephrectomy. Disease progression with recurrent metastases to the third rib and T12 + L1 vertebrae was observed by positron emission tomography-computed tomography (PET-CT) in April 2024. She also had concurrent papillary thyroid carcinoma. Genetic testing confirmed sensitivity to dostarlimab-gxly and pembrolizumab, leading to the initiation of pembrolizumab (200 mg Q3W) and lenvatinib (20 mg QD) in June 2024 after spine surgery. Treatment-related skin toxicities prompted a dose reduction to pembrolizumab 100 mg and lenvatinib 10 mg, but persistent discomfort led to lenvatinib discontinuation in December 2024, with symptom improvement. PET-CT in October 2024 revealed significant improvement in metastatic disease, with probable residual malignancy in the left third rib and posterior pleura, whereas recent follow-up PET-CTs in April and November 2025 showed significantly decreased ¹⁸F-fluorodeoxyglucose avidity in the spine and ribs compared with prior studies. She was admitted for her 30th Keytruda cycle in February 2026, with stable vital signs, normal tumor markers, and no post-infusion adverse reactions. Conclusions: We present a 57-year-old female patient initially diagnosed with FIGO Stage 2 EC, who subsequently developed distant metastases and was restaged as FIGO Stage 4B recurrent disease. The management of this patient illustrates the multimodal treatment approach and the critical role of molecular subtyping in guiding immunotherapeutic strategies for recurrent advanced EC.