Inclusion Criteria:

• Diagnosis: Solid tumors, including central nervous system tumors, that are recurrent or refractory to standard therapy or for which there is no standard therapy. Histologic verification of diagnosis is required.
• Age: < 21 years of age at the time of original diagnosis
• Life expectancy: at least 8 weeks
• Performance status: Karnofsky > 50% for > 10 Lansky > 50% for children < 10 years of age.
• Organ Function: Must have adequate organ and marrow function
• Prior Therapy: Patient must have fully recovered from the acute toxic effects of all prior therapy prior to enrolling on study.
• Must not have current or recent use of full-dose anticoagulants
• Must not have received medications known to inhibit platelet function or known to selectively inhibit cyclooxygenase-2 (COX-2) activity
• Bevacizumab and sorafenib should not be administered to pregnant women.
• Pregnancy tests must be obtained in girls who are > 10 years of age or post-menarchal.
• Males or females of reproductive potential may not participate unless they have agreed to use an effective contraceptive method.
• Breast feeding should be discontinued if a mother wishes to participate in this study.
• Patients with a documented, chronic non-healing wound, ulcer, or bone fracture or history of a major surgical procedure or significant traumatic injury within 28 days prior to beginning therapy should be excluded due to preclinical evidence supporting the potential for delayed wound healing.
• Patients must not have a deep venous or arterial thrombosis (including pulmonary embolism) within the last three months prior to study entry, and must not have a known thrombophilic condition
• Patients must not have a history of myocardial infarction, severe or unstable angina, or severe peripheral vascular disease.
• Ability to understand and willingness of research participant or legal guardian/representative to give written informed consent.

Exclusion Criteria:

• Body surface area < 0.3 m2
• Presence of a known bleeding diathesis or coagulopathy
• Patients with intra-tumoral central nervous system hemorrhage. Patients are required to have a head CT or MRI within 2 weeks of enrollment.
• Patients with known hypersensitivity to other recombinant human antibodies
• Patients who have an uncontrolled infection
• Patients with recurrent or refractory leukemia will be excluded from the dose escalation component of the phase I trial.