There is a need for better visualization of resection margins during surgery for soft tissue sarcoma. Optical molecular imaging of soft tissue sarcoma associated biomarkers is a promising technique to accommodate this need. The biomarker Vascular Endothelial Growth Factor (VEGF-A) is overexpressed in soft tissue sarcoma versus normal tissue and has proven to be a valid target for molecular imaging. VEGF-A can be targeted by the monoclonal antibody bevacizumab. Monoclonal antibodies can be labeled by the near-infrared (NIR) fluorescent dye IRDye800CW (800CW). The investigators hypothesize that bevacizumab-800CW accumulates in VEGF expressing cancer, enabling soft tissue sarcoma visualization using a NIR intraoperative camera system. In this pilot intervention study the investigators will determine the optimal dosage of bevacizumab-800CW (10, 25 or 50mg) to detect soft tissue sarcoma intraoperatively.

Inclusion Criteria:

• Age ≥ 18 years.
• Patients with soft tissue sarcoma who are scheduled to undergo surgical intervention with curative intent
• World Health Organization (WHO) performance score 0-2.
• Signed written informed consent

Exclusion Criteria:

• Medical or psychiatric conditions that compromise the patient's ability to give informed consent.
• Other invasive malignancy
• Pregnant or lactating women. Documentation of a negative pregnancy test must be available for woman of childbearing potential. Woman of childbearing potential are pre- menopausal women with intact reproductive organs and women less than two years after menopause.
• History of infusion reactions to bevacizumab or other monoclonal antibody therapies.
• Inadequately controlled hypertension with or without current antihypertensive medications
• Within 6 months prior to inclusion: myocardial infarction, Transient Ischemic Attack, Cerebral Vascular Accident, pulmonary embolism, uncontrolled chronic hepatic failure, unstable angina pectoris.