Conatumumab/Panitumumab Combination Metastatic Colorectal Cancer Study

Inclusion Criteria: * Histologically or cytologically confirmed metastatic adenocarcinoma of the colon or rectum * Radiographically documented disease progression per modified Response Evaluation Criteria in Solid Tumors (RECIST) during or following treatment with fluoropyrimidine, irinotecan, and/or oxaliplatin chemotherapy for Metastatic Colorectal Cancer. Progressive disease must be documented during or ≤ 6 months after the last dose of the most recent chemotherapy regimen prior to enrollment. * At least 1 uni-dimensionally measurable lesion measuring ≥ 20 mm in one dimension per modified RECIST. Lesion must not be chosen from a previously irradiated field, unless there has been documented disease progression in that field after irradiation and prior to enrollment. All sites of disease must be evaluated. * Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 * Available archived paraffin-embedded tumor tissue from the primary tumor or metastasis for submission to the central laboratory * Man or woman ≥ 18 years of age at the time of enrollment * Hematologic function within the following limits: * Absolute neutrophil count (ANC) \> 1.0 x 10\^9 cells/L * Platelets ≥ 100 x 10\^9/L * Renal function within the following limits: * Creatinine \< 2.0 mg/dL * Hepatic function within the following limits: * Aspartate aminotransferase (AST) ≤ 2.5 x upper limit of normal (ULN) (≤ 5 x ULN if liver metastases) * Alanine aminotransferase (ALT) ≤ 2.5 x ULN (≤ 5 x ULN if liver metastases) * Bilirubin ≤ 2 x ULN * Metabolic function within the following limits: * Amylase ≤ 2 x ULN * Lipase ≤ 2 x ULN * Magnesium ≥ lower limit of normal * Negative pregnancy test ≤ 72 hours before enrollment (for woman of childbearing potential only) * Must have received 1, 2, or 3 prior chemotherapy regimens for Metastatic Colorectal Cancer * Competent to comprehend, sign, and date the independent ethics committee/institutional review board (IEC/IRB) approved written informed consent Exclusion Criteria: * History of other primary cancer, unless: * Curatively resected non-melanomatous skin cancer * Curatively treated cervical carcinoma in situ * Other primary solid tumor curatively treated with no known active disease present and no treatment administered for ≥ 5 years before enrollment * Prior treatment with anti-epidermal growth factor receptor (EGFr) inhibitors (eg, cetuximab, erlotinib, gefitinib), unless treatment was received in the adjuvant setting ≥ 6 months before enrollment * Use of systemic chemotherapy and radiotherapy ≤ 30 days before enrollment * Use of prior anti-tumor therapies with a short serum half-life (less than 1 week) including prior experimental agents or approved anti-tumor small molecules ≤ 30 days before enrollment * Use of anti-tumor therapies with a longer serum half-life (eg, bevacizumab) including prior experimental or approved protein/antibodies ≤ 42 days before enrollment * Any investigational agent or therapy ≤ 30 days before enrollment * Known allergy or hypersensitivity to any component of panitumumab and/or AMG 655 * History of or known presence of central nervous system (CNS) metastases * History of interstitial lung disease (eg, pneumonitis, pulmonary fibrosis) or evidence of interstitial lung disease on baseline chest computerized tomography (CT) scan * Clinically significant cardiovascular disease (including myocardial infarction, unstable angina, symptomatic congestive heart failure, serious uncontrolled cardiac arrhythmia) ≤ 1 year before enrollment * Active inflammatory bowel disease or other active bowel disease causing chronic diarrhea (defined as ≥ Common Terminology Criteria for Adverse Events \[CTCAE\] grade 2 \[CTCAE version 3.0\]) * Known positive test for human immunodeficiency virus (HIV) infection, hepatitis C virus, acute or chronic hepatitis B infection * Any co-morbid disease or condition that could increase the risk of toxicity (eg, significant ascites, significant pleural effusion) * Any uncontrolled concurrent illness (eg, infection, bleeding) or history of any medical condition that may interfere with the interpretation of the study results * Major surgical procedure (requiring general anesthesia) ≤ 28 days or minor surgical procedure (excluding central venous catheter placement) ≤ 14 days before enrollment. Patients must have recovered from surgery related toxicities. * Other investigational procedures are excluded * Patient is currently pregnant or breast feeding * Man or woman of childbearing potential who is not willing to use adequate contraceptive precautions during treatment and for 6 months (for women) or 1 month (for men) after the last investigational product administration. Adequate contraceptive precautions includes double barrier contraceptive methods (eg, diaphragm and condom) or abstinence. * Previously enrolled into this study * Patient unwilling or unable to comply with study requirements