Treatment of Superficial Voluminous Complicated Slow-flow Vascular Malformations With Sirolimus: a Phase 2 Trial in Children Observational-phase Designed

Vascular anomalies include a heterogeneous group of disorders of newborns and children. While infantile hemangioma are common (10% of infants), generally not complicated and easily managed, the majority of other vascular anomalies are rare (<2% altogether) and have no guidelines for management. The most recent classification, adopted by International Society for the Study of Vascular Anomalies (ISSVA) in 1996, divides these lesions into two broad categories: vascular tumors and vascular malformations. Vascular malformations (VMs) are subdivided into high-flow VM and slow-flow VM.

Slow-flow VMs consist of congenital anomalies which may involve abnormal capillaries vessels, venous vessels, lymphatic vessels or combination of several of them. They can be superficial (involving cutaneous and subcutaneous tissues) and/or may have visceral involvement. They can be limited or diffuse, and are sometimes components of genetic hypertrophic syndromes. They always result from defective embryologic vasculogenesis.

The diagnosis of slow-flow VMs is performed on physical examination - a biopsy may be required for confirmation -, and is completed with imaging, which includes ultrasonography and magnetic resonance imaging (MRI). Slow-flow VMs may be simple to manage or can be complicated for several reasons: they may be particularly voluminous; associated with underlying hypertrophy responsible for functional impairment; painful; associated with seepage or continuous cutaneous bleeding; complicated with visceral signs or hematologic disturbances (anemia, thrombopenia). Management requires dedicated multispecialty care. There are no guidelines for treatment, and management may include no intervention - but natural history of these VMs is progressive worsening -, compression by physical bandage, sclerotherapy, resection (when feasible), anti-inflammatory or anti-coagulation drugs.

The vast majority of literature reporting medical therapies consists of paediatric case reports, and is complicated by publication bias, inconsistent use of nomenclature and absence of clinical trials. 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.

Randomized observational-phase design (Feldman et al. J Clin Epidemiol 2001;54:550-557):