Pembrolizumab and Radiotherapy for Platinum-refractory Recurrent Uterine Carcinosarcoma With an Abscopal Effect: A Case Report.

BACKGROUND Immune responses due to radiotherapy and immune checkpoint inhibitors potentially have synergistic effects. CASE REPORT Here, we report a 65-year-old Japanese woman presenting with high-grade endometrial cancer. She was diagnosed with carcinosarcoma, stage IB. A month post-surgery, lung, and mediastinal lymph node metastasis/recurrence was detected. Progressive disease (with high microsatellite instability) with local recurrence and bone metastasis was detected after six chemotherapy cycles with paclitaxel and carboplatin. After combination therapy with pembrolizumab (2 mg/kg, tri-weekly, 10 cycles) and pelvic radiotherapy (30 Gy/10 fractions), enhanced computed tomography revealed a complete response. The patient survived for 14 months with the residual tumour post-relapse. This is the first case of a complete response of recurrent endometrial carcinosarcoma upon combinatorial pembrolizumab and radiotherapy. CONCLUSION Combinatorial immune checkpoint inhibitors and local radiotherapy cause the abscopal effect and may be a promising treatment strategy for advanced or recurrent carcinosarcomas refractory to traditional chemotherapy.