Immunotherapy is an exciting development in cancer treatment, but has not yet made its mark in sarcoma. The resistance of sarcoma to immunotherapy might be related to the presence of macrophages –a type of immune cell. Here, we aim to understand why sarcomas are full of macrophages, and how macrophages impede the immune system. We will determine how radiation therapy, which is commonly used for patients before surgery, affects these phenomena. Our ultimate goal is to design clinical trials to test drugs targeting macrophages in combination with radiation to make immunotherapy relevant for sarcoma.