A Study of Olaratumab (LY3012207) in Participants With Soft Tissue Sarcoma

Inclusion Criteria:

* Have a histologically confirmed diagnosis of STS for which olaratumab and doxorubicin would be appropriate therapy. Participants with a diagnosis of Grade 1 liposarcoma are eligible if there is histological or radiographic evidence of evolution to more aggressive disease. Participants with Kaposi's sarcoma and gastrointestinal stromal tumors (GIST) will be excluded. Participants must have potentially resectable disease (as assessed by the study investigator) and have a primary tumor lesion deemed amenable to serial biopsy.
* For radiotherapy addendum only: Have a histologically confirmed diagnosis of STS of the extremities, Grade 2 or 3, \>5 centimeters, for which olaratumab and radiotherapy would be appropriate therapy. Participants with Kaposi's sarcoma, GIST or myxoid liposarcoma will be excluded.
* Have consented to undergo mandatory serial peripheral whole blood and tumor tissue sampling.

Exclusion Criteria:

* Have active central nervous system (CNS) or leptomeningeal metastasis (brain metastasis) at the time of enrollment. Participants with a history of a CNS metastasis previously treated with curative intent (for example, stereotactic radiation or surgery) that have not progressed on follow-up imaging, have been asymptomatic for at least 60 days and are not receiving systemic corticosteroids and or/anticonvulsants, are eligible. Participants with signs or symptoms of neurological compromise should have appropriate radiographic imaging performed before enrollment to rule out brain metastasis.
* Have received prior treatment with doxorubicin, epirubicin, idarubicin, and/or other anthracyclines or anthracenediones; the participant has received treatment with olaratumab or has participated in a prior olaratumab trial.
* For radiotherapy addendum only: Have received previous radiotherapy in the primary tumor lesion and/or prior treatment with olaratumab or has participated in a prior olaratumab trial.