Primary analysis of pembrolizumab combined with chemotherapy in platinum-sensitive recurrent low-grade serous ovarian cancer: The NOGGO PERCEPTION phase II study.

5595 Background: Low-grade serous ovarian cancer (LGSOC), a rare ovarian malignancy, exhibits a very limited responsiveness to chemotherapy. There is a pressing need for new therapeutic combinations with modern agents to enhance response rates and prognosis in this patient subgroup. Immune checkpoint inhibitors offer a promising pathway, having shown effectiveness in various malignant diseases, including selected cases of ovarian cancer. If our trial should show pembrolizumab effectivity in LGSOC, it would be a signal and impulse for future clinical studies in this rare disease. Methods: This multi-center, single-arm phase II study evaluates pembrolizumab in combination with platinum-based chemotherapy (carboplatin plus pegylated liposomal doxorubicin [PLD] or carboplatin plus gemcitabine) and as maintenance therapy in recurrent LGSOC. Eligible patients include those with disease progression or recurrence ≥6 months post prior platinum-based therapy and ECOG performance status 0-1. The primary endpoint is the 12-month progression-free survival (PFS) rate. Secondary endpoints include response rate (RR), PFS and ORR based on Ki67 expression. Using Simon’s two-stage design, 33 patients were enrolled. Success is defined as ≥11 patients achieving 12-month PFS. Assuming a true PFS rate of 40%, the study has 5% type I error and 80% power. Results: Data from 33 patients were evaluated. At data cut-off, 12 patients were progression free at 12-months (median PFS 15.5 months) while 19 patients progressed or died within 12 months (median PFS 5.6 months). Overall PFS median was 8.4 months. Comparing the subgroups of pre-treatment Ki67 expression