Infantile hemangioma: challenges, new insights, and therapeutic promise.

Infantile hemangiomas are the most common tumors of infancy. They follow a predictable clinical course, beginning in the first 2 weeks of life with a proliferative phase, dominated by rapidly proliferating endothelial cells, lasting for up to a year. Over the next 7 to 10 years (involuting phase), proliferation is reduced, apoptosis increases, and growth of the lesions slows down and finally stops. The regressed lesion may leave behind flabby fatty tissue in place of an often disfiguring lesion, but many involuted lesions will leave the patient without the need for any corrective surgery. About 20% of hemangiomas are extremely disfiguring and destructive to normal tissue and may even be life threatening. In the last several years, much has been learned about molecular features of hemangioma and hemangioma-derived endothelial cells cultured in vitro, but the specific etiology remains unclear. The abundance of molecular clues from educated guesswork, histology, molecular screening studies, and immunohistochemistry with antibodies against specific proteins have prompted much speculation about the biochemical defect underlying hemangiogenesis, and many pathogenetic mechanisms have been proposed. This review summarizes the current state of knowledge about hemangioma, highlighting the proposed mechanisms that are best supported by the available data and the implications for therapeutic advances.