Additional Study Information: The purpose of this study is to evaluate the safety and effectiveness of the study drug called atezolizumab in patients with alveolar soft part sarcoma. Atezolizumab works by unblocking your immune system, allowing your immune system cells to recognize and then attack your tumor cells. Atezolizumab could shrink your cancer but it could also have side effects. Researchers hope to learn if the study drug will shrink the cancer by at least one-quarter compared to its present size. Atezolizumab is approved for use by the Food and Drug Administration (FDA) for a specific type of cancer, but it is not FDA-approved for your type of tumor and is still an experimental drug.