A Study of Olaratumab (IMC-3G3) in Prostate Cancer

Inclusion Criteria:

* histologically-confirmed adenocarcinoma of the prostate
* radiographic evidence of metastatic prostate cancer (Stage M1 or D2)
* has prostate cancer unresponsive or refractory to medical or surgical castration with a serum testosterone level of \<50 nanograms per milliliter (ng/mL)
* has had disease progression or intolerance on docetaxel-based therapy
* prostate-specific antigen (PSA) ≥10 ng/mL
* all clinically significant toxic effects of prior surgery, radiotherapy, chemotherapy or hormonal therapy have resolved to ≤Grade 1, based on National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE) version (v) 4.02
* participant has an Eastern Cooperative Oncology Group (ECOG) Performance Status 0-2
* adequate hematologic function
* adequate hepatic function
* adequate renal function
* urinary protein is ≤1 on dipstick or routine analysis
* life expectancy of more than 3 months
* fertile man with partners that are women of childbearing potential must use an adequate method of contraception during the study
* signed Informed Consent Document

Exclusion Criteria:

* concurrent active malignancy other than adequately treated nonmelanomatous skin cancer or other noninvasive or in situ neoplasms
* The participant has received more than 1 prior cytotoxic chemotherapy regimen for metastatic disease
* prior therapy with mitoxantrone for advanced prostate cancer
* The participant has a history of symptomatic congestive heart failure or has a pre study echocardiogram or multigated acquisition scan with left ventricular ejection fraction that is ≥10% below the lower limit of normal institutional range
* history of prior treatment with other agents that directly inhibit platelet-derived growth factor (PDGF) or platelet-derived growth factor receptors (PDGFR)
* known allergy to any of the treatment components: olaratumab, mitoxantrone, and/or prednisone
* radiotherapy within 21 days prior to first dose of olaratumab
* any investigational therapy within 30 days of randomization
* is receiving corticosteroids at a dose \>5 mg prednisone PO BID or equivalent
* received prior strontium-89, rhenium-186, rhenium-188, or samarium-153 radionucleotide therapy and has either ongoing evidence of bone marrow dysfunction or poorly controlled bone pain
* has any ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, serious cardiac arrhythmia, psychiatric illness, active bleeding or pathological condition that carries a high risk of bleeding, or any other serious uncontrolled medical disorders
* known or suspected brain or leptomeningeal metastases
* known human immunodeficiency virus infection or acquired immunodeficiency syndrome-related illness