The formation of chaotic microvascular network in B16 xenografts.

<p>(<b>A</b>) The interconnection of initial endothelial cells that had penetrated into tumor tissue. (B) Schematic diagram showing the forming and formed endothelial loops. (C) The dynamic process of more and more endothelial loops assembling into a complex vascular network. Angiogenic sprouts were indicated by arrows, the formed endothelial loops were indicated by crosses. (D) Endothelial loops varied significantly in size and shape. The B16 xenograft is indicated by arrow (E). Scale bars, 200 µm.