Hematoxylin and eosin (H&E) stained sections of proliferating, involuting and involuted phases of IH. The proliferating phase is characterized by densely packed tumor cells that form immature vessels (A). In the involuting phase, disorganized vasculature consists of flat endothelium and pericytes (B). The tumor is replaced by fat and/or connective tissues in the involuted phase (C). Scale bar = 100 μm.