A Study of Olaratumab (LY3012207) Plus Pembrolizumab in Participants With Advanced or Metastatic Soft Tissue Sarcoma

Inclusion Criteria:

* Histologically confirmed diagnosis of advanced unresectable or metastatic STS, not amenable to curative treatment and after available standard therapies have failed to provide clinical benefit. Note: Participants with a diagnosis of Grade 1 liposarcoma (atypical lipomatous neoplasms) are eligible if there is histological or radiographic evidence of evolution to more aggressive disease.
* Presence of measurable or nonmeasurable but evaluable disease as defined by the Response Evaluation Criteria in Solid Tumors (RECIST 1.1).
* Performance status 0-1 on the Eastern Cooperative Oncology Group (ECOG) scale.
* Must be able to provide tumor tissue obtained within 6 months of study enrollment. If such tissue is not available, a newly obtained core or excisional biopsy of a tumor lesion must be performed.
* Have an anticipated life expectancy of ≥3 months.

Exclusion Criteria:

* Have received any previous systemic therapy (including investigational agents) targeting PD-1/programmed cell death ligand 1 (PDL-1) or PD-1/PDL-2 signaling pathways (including previous participation in Merck MK-3475 trials). Prior treatment with olaratumab is allowed. Prior therapy with other immune checkpoint inhibitors, including but not limited to, anti-CD137 antibody or anti-cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) antibody, is not permitted.
* Have known active central nervous system (CNS) metastasis and/or carcinomatous meningitis. Participants with treated CNS metastases are eligible for this study if they have not received corticosteroids and/or anticonvulsants within 7 days of study treatment, and their disease is asymptomatic and radiographically stable for at least 60 days.
* Have active autoimmune disease or other syndrome that requires systemic steroids or autoimmune agents in the past 2 years.
* History of interstitial lung disease or non-infectious pneumonia.
* Have received a live-virus vaccine within 30 days prior to planned treatment start.
* Have histologically or cytologically confirmed Kaposi's sarcoma or gastrointestinal stromal tumor (GIST).
* Have inflammatory bowel disease for which the participant has used immunosuppressive agents within the last 2 years.