Case reports and series have provided evidence for supporting the need for a clinical trial of sirolimus by reporting successful treatment on several children with complicated vascular anomalies. The choice of sirolimus is rational. Mammalian target of rapamycin (mTOR) is a serine/threonine kinase regulated by phosphoinositide-3-kinase involved in cell mobility, cell growth and angiogenesis. Sirolimus inhibits mTOR, which induces inhibition of angiogenesis, in particular lymphangiogenesis, which has been demonstrated in several models.