Metastasis is the leading cause of cancer-related mortality; however, a complete understanding of the molecular programs driving the metastatic cascade is lacking. Metastasis is dependent on collective invasion—a developmental process exploited by many epithelial cancers to establish secondary tumours and promote widespread disease. The key drivers of collective invasion are “Leader Cells”, a functionally distinct subpopulation of cells that direct migration, cellular contractility, and lead trailing or follower cells. While a significant body of research has focused on leader cell biology in the traditional context of collective invasion, the influence of metastasis-promoting leader cells is an emerging area of study. This review provides insights into the expanded role of leader cells, detailing emerging evidence on the hybrid epithelial–mesenchymal transition (EMT) state and the phenotypical plasticity exhibited by leader cells. Additionally, we explore the role of leader cells in chemotherapeutic resistance and immune evasion, highlighting their potential as effective and diverse targets for novel cancer therapies.

OVCAR3 cells are widely used to establish animal models of high-grade serous ovarian cancer (HGSOC) via subcutaneous (SC), intraperitoneal (IP), and intrabursal (IB) routes. However, direct comparisons of tumour development across these implantation routes are limited. This study compared the establishment, progression, dissemination and histological characteristics of SC, IP and IB OVCAR3 xenografts in female athymic nude mice over defined route-specific assessment periods. Tumour development was evaluated using semi-quantitative tumour scoring, histological assessment, nuclear morphometry and immunofluorescence staining for PAX8, WT1 and Ki67. IP and IB routes achieved 100% engraftment whereas SC implantation achieved engraftment in 15 of 18 animals. IP produced rapid carcinomatosis by Week 2, IB produced localised ovarian growth before contralateral spread, and SC produced confined stromal-encapsulated tumours. Mechanical confinement in the IB niche increased intratumoural density (1087 cells/mm²) and compressed single-cell nuclear area (22 µm²) compared to IP/SC models. Histological and immunofluorescence assessment demonstrated tumour expression of PAX8, WT1 and Ki67 across the three models, with route-associated differences in tumour organisation and staining distribution. Nuclear morphometric measurements varied among the models, although the between-route differences were not statistically significant. Together, these findings define the principal characteristics and progression patterns of three commonly used OVCAR3 implantation models and provide a practical framework for selecting the route and experimental timeframe most appropriate to the aims of future studies.