This phase II trial studies how well atezolizumab works in treating patients with alveolar soft part sarcoma that has not been treated, has spread from where it started to other places in the body and cannot be removed by surgery. Monoclonal antibodies, such as atezolizumab, may allow the immune system cells to find and kill the tumor cells.
I. Determine the objective response rate (ORR) using Response Evaluation Criteria in Solid Tumors (RECIST) version (v) 1.1 of atezolizumab in patients with advanced alveolar soft part sarcoma (ASPS) in adult subjects >= 18 years and in pediatric/adolescent subjects >= 6 years.
I. Determine duration of response (DOR) using RECIST v 1.1 and/or change in clinical symptoms.
II. Measure progression-free survival (PFS) time as determined by investigator using RECIST v 1.1.
III. At the Clinical Center, National Cancer Institute (NCI), only: correlate response with expression of potential immune biomarkers in paired biopsies.
IV. Compare the RECIST v 1.1 versus (vs) the immune-related response criteria (irRC) in patients with ASPS on atezolizumab.
Patients receive atezolizumab intravenously (IV) over 30-60 minutes on day 1. Courses repeat every 21 days in the absence of disease progression or unacceptable toxicity.
After completion of study treatment, patients are followed up for 4 weeks.