Study to Evaluate Mechanisms of Acquired Resistance to Panitumumab

Inclusion Criteria: * Histologically or cytologically confirmed metastatic adenocarcinoma of the colon or rectum; * Subjects with wild-type KRAS tumor status confirmed by an Amgen approved central laboratory assessment or an experienced local laboratory assessment of archival tumor tissue (preferably from the primary tumor); * Radiographic evidence of disease progression while on or ≤ 6 months after completion of treatment with irinotecan- and oxaliplatin- or oxaliplatin-based chemotherapy for mCRC; * Radiographic measurement of tumor burden done within 28 days prior to Day 1 (start of treatment with investigational product); * At least 1 uni-dimensionally measurable lesion ≥ 20 mm using conventional computed tomography (CT) or magnetic resonance imaging (MRI) or ≥ 10 mm by spiral CT scan per modified RECIST v1.0. 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; * At least 1 tumor (preferably a metastasis or unresected primary tumour) that is amenable to core biopsy, as determined by the clinician who will perform the biopsy; * Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1; * A life expectancy estimate of ≥ 3 months; * Willing to undergo two serial core biopsy procedures of tumors (metastasis or unresected primary); * other criteria may apply Exclusion Criteria: * History of other primary cancer, unless: * Malignancy treated with curative intent and with no known active disease present for ≥ 3 years before enrollment and felt to be at low risk for recurrence by the treating physician, * Adequately treated non-melanomatous skin cancer or lentigo maligna without evidence of disease, * Adequately treated cervical carcinoma in situ without evidence of disease, * Prostatic intraepithelial neoplasia without evidence of prostate cancer; * History of prior or concurrent central nervous system (CNS) metastases; * Prior treatment with anti-EGFR (eg, panitumumab, cetuximab or small molecule inhibitors (eg, erlotinib, gefitinib); * Prior treatment with monoclonal antibodies directed against insulin-like growth factor-1 receptor (IGF-1R) or small molecule inhibitors directed against IGF-1R; * Use of systemic chemotherapy or radiotherapy ≤ 21 days before enrollment. Subjects must have recovered from acute toxicities related to radiotherapy; * Use of any antibody therapy (eg, bevacizumab) ≤ 42 days before enrolment; * Use of anti-tumor therapies including prior experimental agents or approved anti-tumor small molecules ≤ 30 days before enrolment; * Known allergy or hypersensitivity to any component of panitumumab, irinotecan, or AMG 479; * Known uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) polymorphisms predisposing to increased irinotecan toxicity; * History of irinotecan intolerance that may interfere with planned treatment; * History of interstitial lung disease (eg, pneumonitis, pulmonary fibrosis) or evidence of interstitial lung disease on baseline chest CT scan; * Clinically significant cardiovascular disease (including myocardial infarction, unstable angina, symptomatic congestive heart failure, serious uncontrolled cardiac arrhythmia) ≤ 1 year before enrolment; * Active inflammatory bowel disease or other active bowel disease causing chronic diarrhea (defined as ≥ grade 2 per Common Terminology Criteria for Adverse Events (CTCAE) version 3.0); * Known positive test(s) for human immunodeficiency virus (HIV) infection, hepatitis C virus, acute or chronic active hepatitis B infection; * Major surgical procedure ≤ 28 days before enrollment or minor surgical procedure ≤ 14 days before enrollment. Subjects must have recovered from surgery related toxicities. Core biopsy, central venous catheter placement, fine needle aspiration, thoracentesis, or paracentesis is not considered a major or minor surgical procedure; - Other investigational procedures or drugs (ie, participation in another clinical study) ≤ 30 days before enrolment; * other criteria may apply