Response of undifferentiated and dedifferentiated endometrial cancer to pembrolizumab: a case report.

To report our experience with pembrolizumab in undifferentiated and dedifferentiated endometrial cancer. We performed an institutional review board-approved, retrospective study of computerized pharmacy records to identify all patients with undifferentiated and dedifferentiated endometrial carcinomas treated with pembrolizumab. Eleven patients who received pembrolizumab were identified with the following stages: International Federation of Gynecology and Obstetrics stages IC (1), IIC (2), IIIB (2), IIIC2 (2), and IVB (4). One hundred and forty cycles of pembrolizumab were administered. Ten of the 11 patients were mismatch repair (MMR)-deficient. Eight of the patients received pembrolizumab in combination with chemotherapy. Three partial and two complete responses were seen. Both complete responses were seen when pembrolizumab was given with chemotherapy. Four patients were treated in the adjuvant setting with pembrolizumab had no measurable disease and were not evaluable for response but remain disease-free. Two treatment-emergent adverse effects were noted: colitis and hepatitis. Because of the very high rate of MMR deficiency in undifferentiated and dedifferentiated endometrial carcinomas, incorporation of immunotherapy to chemotherapy should strongly be considered in patients with this histologic type in advanced and early-stage disease.