Purpose: The management of endometrial carcinoma no longer amenable to treatment with surgery or radiotherapy has not improved significantly with modern chemotherapy. Alternative therapeutic options are desperately needed.

Experimental Design: We describe 2 heavily pretreated patients with recurrent disease refractory to surgery, radiotherapy, and chemotherapy who were treated with the anti–PD-1 immune checkpoint inhibitor nivolumab.

Results: Patient #1 harbored an ultra-mutated tumor (mutation load/MB = 117.3, total mutations = 4,660) driven by mutation in the exonuclease domain of the DNA polymerase ϵ gene. Patient #2 harbored a hyper-mutated tumor (mutation load/MB = 33.5, total mutations = 1,037) due to a germinal MSH6 gene mutation. Both patients demonstrated a remarkable clinical response to the anti–PD-1 immune checkpoint inhibitor nivolumab. Patients' clinical responses remain unchanged at the time of the writing of this report, with no grade 3 or higher side effects reported to date.

Conclusions: Anti–PD-1 inhibitors represent a novel treatment option for recurrent/metastatic, ultra/hyper-mutated human tumors refractory to salvage treatment. Clin Cancer Res; 22(23); 5682–7. ©2016 AACR.

See related commentary by Piulats and Matias-Guiu, p. 5623