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INTRODUCTION: High-grade serous ovarian cancer (HGSC), the most lethal subtype of epithelial ovarian cancer (EOC), often originates from serous tubal intraepithelial carcinoma (STIC) and is typically diagnosed at advanced stages. However, the mechanisms underlying the dissemination of STIC cells into the peritoneal cavity remain poorly understood. This study aims to clarify whether the immune microenvironment triggered by physiological ovulation contributes to this early metastatic process. METHODS: We investigated the link between ovulation-induced peritoneal neutrophil extracellular trap (NET) formation, NETosis, and cancer cell seeding. Peritoneal fluid from humans and mice at various ovulatory stages was analyzed for immune cell composition. NETosis was assessed by neutrophil DNA staining and detection of PAD4 and citrullinated histone H3 (CitH3). STIC-mimicking and HGSC cells were used with or without NET inhibition to evaluate effects on early metastatic seeding. RESULTS: Ovulatory follicular fluid (FF) robustly induced peritoneal neutrophil recruitment and rapid NET formation via a G-CSF-mediated, ROS/NOX/PAD4-dependent mechanism. NETs promoted cell clustering and anchorage-independent growth through extracellular DNA, while NET-derived soluble factors enhanced cell adhesion and invasion. In vivo, exposure to FF enhanced early intraperitoneal tumor cell seeding, which was significantly reduced by PAD4 inhibition. CONCLUSION: Physiological ovulation induces neutrophil influx and NETosis, creating a pro-metastatic peritoneal niche that facilitates both the dissemination and transformation of STIC cells. These findings reveal a novel mechanism linking ovulation to HGSC progression and suggest NETosis as a potential target for early intervention.
Chu et al. (Sun,) studied this question.