Clinical implications of immune checkpoint inhibitor in chemotherapy-resistant advanced endometrial cancer with a pathogenic POLE mutation: a case report

The POLE -ultramutated subtype of endometrial cancer is associated with a favorable prognosis and is most frequently presents at an early stage. Even in advanced disease, which is uncommon, available data suggest favorable outcomes and a potentially limited incremental benefit of immunotherapy. We report a case of chemotherapy-resistant, POLE -mutated advanced endometrial cancer that showed a remarkable and durable response to immunotherapy. A 54-year-old woman was diagnosed with stage IVB endometrial cancer (endometrioid carcinoma, grade 3). Despite first-line therapy consisting of paclitaxel plus carboplatin and cytoreductive surgery, the disease progressed. Subsequent doxorubicin plus cisplatin chemotherapy also failed to achieve an objective response. Comprehensive genomic profiling revealed a pathogenic POLE mutation (p.V411L) with a markedly elevated tumor mutational burden of 174 mutations/Mb, while the tumor was microsatellite stable. Pembrolizumab was initiated, resulting in substantial regression of peritoneal metastases and multiple lymph node metastases. Although treatment was interrupted because of immune-related adverse events, disease has remained controlled for more than 2 years after discontinuation. This clinical course suggests that timely comprehensive genomic profiling may provide clinically actionable molecular information to guide treatment modification, even in advanced POLE -mutated endometrial cancer showing chemotherapy resistance. It also highlights that immunotherapy may play an important role in achieving durable disease control in this molecularly defined subset.