Tumor-induced radial vascular patterning in the chick chorioallantoic membrane

Tumor implantation on the chick chorioallantoic membrane (CAM) produces a characteristic radial or "starburst" microvascular pattern, classically attributed to tumor angiogenesis factor-driven sprouting. Here, we investigated the structural and functional basis of this pattern using intravital fluorescence microscopy, particle tracking, corrosion casting, scanning electron microscopy, and transcriptional profiling across 13 tumor cell lines. Eight cell lines successfully engrafted; six formed localized tumor masses associated with a rapid, well-defined radial vascular pattern evident within three days, while two exhibited diffuse, infiltrative growth with generalized capillary hypertrophy. Functional imaging revealed preferential flow paths, capillary loops, and U-turn particle trajectories at tumor margins. Structural analysis demonstrated that radial vessels arose predominantly from intussusceptive angiogenesis, with vessel duplication and intraluminal pillar formation, rather than endothelial proliferation alone. In contrast, diffuse tumors lacked radial organization despite robust capillary hypertrophy. Bulk transcriptional profiling failed to identify a distinctive angiogenic gene signature. These findings demonstrate that intussusceptive duplication underlies tumor-induced radial vascular patterning in the CAM.