Monocytes: a possible source of hemangioma endothelial cells

Hemangiomas have a distinctive proliferative phase characterized by rapid proliferation of capillaries within the first year of life, followed by an involuting phase characterized by spontaneous and steady regression of the tumor that may last up to 5-10 years. Angiogenesis has been proposed to be the predominant mechanism of vessel formation in hemangiomas. Emerging evidence shows that endothelial progenitor cells play an important role in the physiological and pathological angiogenesis. However, the numbers of endothelial progenitor cells in hemangioma are small. Recent studies show that large numbers of monocytes, the ancestor of endothelial progenitor cells, are present in hemangioma. In this paper, we hypothesize that monocyte is a possible source of hemangioma endothelial cells according to previous research evidence. This hypothesis suggests that monocytes contribute to early expansion of hemangioma. Further investigation is needed to determine which factors influence the homing and the differentiation of monocytes in hemangioma and potential therapeutic implications of these monocytes.