Tight Spaces, Big Discoveries: Decoding Human Adhesion Biology with Avian Chorioallantoic Membrane Xenograft Models.

Tight junction (TJ) proteins, such as Junctional Adhesion Molecule-A (JAM-A), claudins, and occludin, play increasingly recognized roles in cancer biology beyond their structural functions, influencing tumour proliferation, invasion, metastasis and therapy resistance. Understanding how these proteins modulate tumour progression in vivo requires models that are both physiologically relevant and ethically viable. The chick chorioallantoic membrane (CAM) xenograft model has emerged as a powerful and cost-effective in vivo system that aligns with the 3Rs (replacement, reduction, and refinement), offering unique advantages such as vascular accessibility, rapid tumour growth kinetics and immunotolerance. This review explores how the CAM model can be leveraged to study the mechanistic role of TJ proteins in tumour-stroma interactions, angiogenesis, extracellular matrix (ECM) remodelling and mechanotransduction, including the YAP/TAZ pathway. While limitations remain, particularly with respect to immune modelling and long-term studies, recent advances in imaging, genetic manipulation and integration of patient-derived xenografts (PDXs) are expanding the model's translational relevance. Standardizing methodologies and embracing new molecular tools will further elevate the utility of this approach as a complementary platform to traditional rodent models, with significant promise for TJ-focused cancer research and therapeutic innovation.