De-Escalated Adjuvant Treatment for Advanced MMR Deficient Mixed Endometrioid/Clear Cell Endometrial Carcinoma with PD-1 Inhibition Alone: A Case Report.

Advanced mixed epithelial endometrial carcinomas are rare high-grade cancers with a poor prognosis. A clear cell component infers relative chemotherapy insensitivity, likely further increased by p53 wild type status and MMR deficiency. PD-1 inhibition for MMR deficient endometrial cancers has been recently added to first-line adjuvant treatment in combination with platinum-based chemotherapy. Information on de-escalation of adjuvant treatment to PD-1 inhibition alone without chemotherapy is sparse. Here, we present a patient with advanced stage mixed epithelial endometrial carcinoma, a clear cell component and MMR deficiency who underwent de-escalated adjuvant treatment with PD-1 inhibition alone without simultaneous chemotherapy. Histotype-agnostic adjuvant monotherapy with checkpoint immune inhibitors alone appears to be a highly effective even in the rare mixed endometrial carcinomas if MMR protein deficient as described in this case report.