Complete remission of ovarian clear cell carcinoma achieved after pseudoprogression during PD-1 inhibitor therapy.

Background: Ovarian clear cell carcinoma (OCCC), which is resistant to traditional treatment, has a poor prognosis. Immune checkpoint inhibitors (ICIs) have been emerged in the past decade and are now widely used in clinics. However, OCCC reportedly responds poorly to ICIs, and ICI monotherapy is rarely used for patients with OCCC. Methodology & Results: We report the case of a patient with refractory OCCC who received an ICI (nivolumab) monotherapy treatment and achieved a complete response despite the occurrence of pseudoprogression. Nivolumab was discontinued after 2 years, and the patient remained in complete remission more than a year after treatment withdrawal. Conclusion: This is the first report of complete remission being achieved in a case of refractory OCCC after pseudoprogression during nivolumab monotherapy.