OBJECTIVES:  Soft tissue sarcoma (STS) is a heterogeneous group of rare solid tumors that arise from soft tissues, such as muscle, fat, nerves and blood vessels. The objective of this study is to describe the treatment patterns among patients diagnosed with advanced STS. METHODS:  Newly diagnosed STS patients with at least two ICD-9-CM codes of 171.x on two different days between July 1, 2004 and March 30, 2014 were identified from the Truven MarketScan claims database. The first ICD-9 code was considered the index diagnosis. Due to the absence of disease stage and other clinical variables, patients were assumed to have advanced disease if they had no claims for excision or resection surgery from 30 days prior to the index diagnosis through the end of first-line chemotherapy. RESULTS:  Of 17,009 patients eligible for the study, 4159 (24.5%) received first-line chemotherapy, of whom 1589 (38.2%) patients were advanced STS patients (mean age of 57.9,SD=14.5), 47.8% male and a mean Charlson Comorbidity Score (excluding cancer codes) of 0.6 (SD=1.2). Although there are a limited number of regimens for STS in treatment guidelines, 214 unique first-line treatment regimens were identified in claims data. The most frequently used regimen included unclassified drugs (211(13.3%)). Despite being the standard of care, only 47(2.96%) patients had claims for doxorubicin monotherapy and 99 (6.23%) had claims for doxorubicin combination therapy; 118(7.43%) patients had claims for docetaxel+gemcitabine and 32(2.01%) for gemcitabine monotherapy. CONCLUSIONS:  The chemotherapy regimens used to treat STS patients were heterogeneous and not consistent with prior research. The proportion of patients who received standard-of-care doxorubicin was considerably lower than anticipated. These findings are likely due to the high number of unclassified drug codes and lack of specific ICD-9 codes for STS. These limitations should be considered prior to using claims alone to identify or study STS patients.