Introduction/Background Within the group of invasive epithelial ovarian cancers, low-grade serous ovarian cancer (LGSOC) is a minority. Recent studies have revealed that LGSOC is only moderately sensitive to chemotherapy. No other agents have been approved in LGSOC since the implementation of bevacizumab several years ago. New therapeutic combinations with current chemicals are in high demand to improve the response rate and prognosis in this group of patients. Immune checkpoint inhibitors are a new treatment option that has shown to be successful in a variety of cancers as well as in a subset of ovarian cancer patients. The standard chemotherapy will be administered with pembrolizumab in recurrent LGSOC cases with a treatment free interval (TFI) of more than 6 months after the last platinum-based chemotherapy. There have been no comparable studie completed or planned to the authors knowledge. If our trial demonstrates the efficacy of pembrolizumab in LGSOC, it will serve as a signal and urge for future clinical trials in this rare condition.

Methodology This is a multi-center, single-arm phase 2 study evaluating pembrolizumab therapy in recurrent LGSOC cases in combination with platinum-based chemotherapy (carboplatin plus pegylated liposomal doxorubicin or carboplatin plus gemcitabine) and as maintenance. This clinical trial is open to LGSOC patients who have progressed or recurred at least six months after the last platinum-containing treatment. The perimary objective is to determine the rate of progression-free survival (PFS) after 12 months. The trial will follow Simon’s two-stage design, with a total enrollment of up to 33 patients. In the first phase 18 patients will be enrolled and if at least 5 patients show PFS after 12 months the study is going to be continued with an additional 15 patients. The trial is claimed successful, if at least 11 patients show PFS after 12 months.

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