Kaposiform hemangioendotheliomas (KHE) are extremely rare life threatening tumors which can be associated with Kasabach-Merritt Phenomenon consisting of profound thrombocytopenia and hypofibrinogenemia causing a significant risk of bleeding and an associated mortality rate as high as 20% to 30%. Despite the severity of potential complications, we lack uniform guidelines for the treatment and response to treatment of children and young adults with these tumors. KHE patients have been treated with a multitude of aggressive drug regimens without prospective evaluation of response or safety. Presently, vincristine is considered the standard of practice. We have treated a subset of these patients on study SIR-DA-0901 (FDA Grant# 5RO1FD003712-01). This study is a phase II trial assessing the efficacy and safety of sirolimus for the treatment of complicated vascular anomalies. Although the numbers are small, the response has been extremely promising with excellent tolerability. There is pre-clinical and clinical data supporting the essential regulatory function of the PI3 kinase/AKT/mTOR pathway in vascular growth and organization which suggests a therapeutic target for patients with complicated vascular anomalies. The overall goal of this trial is to objectively assess the efficacy of sirolimus compared to vincristine for the treatment of patients with high risk KHE.

Hypothesis: Sirolimus treatment for children and young adults with Kaposiform hemangioendotheliomas will be more effective than vincristine, assessed by time to response in an induction period and provide equivalent safety parameters.

Study Rationale We propose a multi-center, phase II trial with participation from 8 sites. The study will consist of two phases. The first of these is an initial induction phase in which vincristine and steroids will be compared to sirolimus and steroids. Response in the induction phase will be assessed as time to hematologic response. At the end of induction phase, cross over can occur if there is failure to respond. Part 2 is a maintenance phase which will be 1 year in length. Continued safety and efficacy data will be collected during maintenance and there will be cross over at any time for patients who lose their response following induction. Failure will be defined as worsening of hematological parameters on two separate laboratory evaluations at any time during maintenance or if they meet the definition of progressive disease following response assessments. Formal response in maintenance will be evaluated by imaging studies, functional assessment, and quality of life as per study SIR-DA-0901. Present therapies are very limited and new therapies are desperately needed for this devastating disease. Based on our preliminary data, there is a very good rationale for sirolimus therapy in KHE patients and so a phase II trial is urgently needed to determine if this therapy is to become the new standard of care for KHE patients.

Our secondary aims will be addressing biomarker analysis. There are limited studies describing the biology of these tumors. Per study SIR-DA-0901 there is some preliminary data indicating the importance of VEGF-C and other upregulated markers in the mTor pathway. This needs to be further investigated especially in KHE patients. Furthermore there are no clear objective measurements to determine response data.