Pathologic complete response to immune checkpoint inhibitor in a stage IIIB ovarian clear cell carcinoma patient with POLE mutation resistant to platinum-based chemotherapy: a case report

BACKGROUND: Ovarian clear cell carcinoma (OCCC) is a subtype of ovarian cancer with unique features at histological and molecular levels. The prevalence of OCCC is higher in east Asia than in Western countries. As cases are usually chemo-resistant, treatment effects of platinum-based chemotherapy are not satisfactory, especially for patients with stage III or IV disease. Immune checkpoint inhibitors (ICIs) have revolutionized the treatment of patients with advanced-stage cancers. However, whether advanced OCCC patients benefit from ICIs remains elusive. CASE DESCRIPTION: Herein, we report a Chinese patient with stage IIIB inoperable OCCC who was resistant to platinum-based chemotherapy and anlotinib. Next-generation sequencing (NGS) revealed a pathogenic polymerase epsilon (POLE) P286R mutation and a high level of tumor mutation burden (TMB) in tissue and plasma samples. The ICI sintilimab was then used with bevacizumab as third-line treatment. Tumor reduction was observed, and the patient underwent surgical resection which indicated a pathologic complete response (pCR). Maintenance therapy with sintilimab and bevacizumab was applied, and the patient has achieved overall survival (OS) of 35 months since the diagnosis. They have also achieved a progression-free survival (PFS) of 29 months since commencing ICI treatment and have been disease-free for 24 months after surgical resection. CONCLUSIONS: The treatment effect of ICI in POLE-mutant OCCC patients has been rarely reported. The treatment benefits observed in the stage IIIB OCCC patient who was resistant to platinum-based chemotherapy may be associated with the presence of POLE mutation and a high level of TMB. Comprehensive genomic profiling could contribute to appropriate treatment decisions for OCCC.