Background: Approximately 13,000 cases of soft tissue and bone are diagnosed annually in the US. Despite primary surgery many patients develop recurrent disease. Response rates to chemotherapy are low and new agents are needed. Gene array studies have shown Aurora Kinase A (AURKA) commonly overexpressed. Inhibition of AURKA by shRNA or by a specific AURKA inhibitor blocks in vitro proliferation of multiple sarcoma subtypes. MLN8237 (alisertib) is a novel and oral, ATP-competitive, selective small-molecule inhibitor of AURKA. We hypothesize that alisertib will be an effective treatment for advanced/metastatic sarcoma. Methods: This CTEP-sponsored, investigator-initiated, multi-center phase II study uses alisertib in patients with advanced/metastatic sarcoma and is conducted through the Alliance for Clinical Trials in Oncology (Alliance A091102). Patients must have adequate performance status, organ function, and measurable disease (RECIST v1.1). Patients are enrolled in one of five cohorts, depending on histology: 1) liposarcoma, 2) leiomyosarcoma, 3) undifferentiated sarcoma, 4) malignant peripheral nerve sheath tumor, or 5) other. Patients are treated with alisertib 50mg PO BID d1-d7 every 21 days until either progressive disease or unacceptable toxicity. The primary endpoint is objective overall response rate (ORR). Secondary endpoints include progression-free survival (PFS) and overall survival (OS). Translational objectives include correlation of ORR, PFS and OS with baseline and post-treatment markers of AURKA inhibition in tumor biopsies and baseline and post-treatment [F-18] FLT-PET scans. A Simon two-stage design is used for each of the 5 cohorts and one confirmed response in the first 9 patients expands enrollment in that cohort to 24. Enrollment began in December 2012. As of January 2013, 14 pts have been enrolled. Funded by the Alliance for Clinical Trials in Oncology. Clinical trial information: NCT01653028.