Dramatic response to single-agent atezolizumab in a patient with MSI-H serous ovarian cancer.

What is known and objective Patients with ovarian cancer have not benefited substantially from immunotherapy. We report a case of ovarian cancer, however, that responded well to the programmed cell death-ligand 1 inhibitor atezolizumab. Case summary A 64-year-old woman with recurrent ovarian carcinoma, not responsive to platinum/taxane and bevacizumab therapy, was BRCA normal but showed loss of MLH1 and PMS2 proteins. She was treated with atezolizumab. After the third cycle, her CA 125 levels decreased to normal. Radiologic evaluation showed a near-complete response. What is new and conclusion Identifying response markers is important when choosing therapy for ovarian cancer patients.