Safety and Efficacy Study of MEHD7945A + FOLFIRI Versus Cetuximab + FOLFIRI as Second Line Therapy in Participants With KRAS Wild-Type Metastatic Colorectal Cancer (mCRC)

Inclusion Criteria: * Histologically or cytologically confirmed adenocarcinoma of the colon and/or rectum, with KRAS wild-type status * Progressive disease on or after first-line oxaliplatin-containing regimen for mCRC; participants must have received oxaliplatin-containing chemotherapy for greater than or equal to (\>/=) 3 months; no more than one prior chemotherapy regimen for metastatic disease is allowed * Measurable disease per modified Response Evaluation Criteria in Solid Tumors Version 1.1 (RECIST v1.1) * Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 * Adequate hematologic and end-organ function Exclusion Criteria: * Prior treatment with irinotecan * Prior treatment with an investigational or approved human epidermal growth factor receptor (HER)-targeted agent * Last anti-tumor therapy within 4 weeks prior to Cycle 1, Day 1 * Leptomeningeal disease as the only manifestation of the current malignancy * Active infection requiring intravenous antibiotics * Active autoimmune disease that is not controlled by nonsteroidal anti-inflammatory drugs * Current severe, uncontrolled systemic disease * Known human immunodeficiency virus (HIV) infection * Untreated/active central nervous system metastases (progressing or requiring anticonvulsants or corticosteroids for symptomatic control) * Pregnant or lactating women * Malignancies other than colorectal cancer within 5 years prior to randomization, except for adequately treated basal or squamous cell skin cancer and carcinoma in situ of the cervix