Vascular Biology Program, Children s Hospital Boston and Department of Surgery, Children s Hospital Boston and Harvard Medical
School, Boston, Massachusetts
Hemangioma is a tumor of endothelium that occurs in 5 to 10 percent of caucasian infants. Often referred to as infantile hemangioma, it follows a unique biological course: it proliferates rapidly in the first year of life, regresses slowly during early childhood, and never recurs. These features of hemangioma distinguish it from other vascular tumors, which do not regress and can occur in adults. Like many vascular tumors, the endothelial cells that comprise heman-gioma express a multitude of endothelial markers and angiogenic growth factors. Endothelial cells from hemangiomas are clonal and exhibit abnormal properties when compared to normal human microvascular endothelial cells. These findings strongly suggest that hemangiomas arise when a somatic mutation occurs, within a single endothelial cell, in a gene that controls endothelial cell proliferation and possibly responses to angiogenic stimuli. The molecular mechanisms underlying the rapid growth and the spontaneous involution of hemangioma are yet to be discovered, but when elucidated, are likely to yield unique insights into the regulation of blood vessel formation and growth.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.