Overall survival was defined as the time from the randomization date to the date of death. Participants who had not died by the analysis data cut-off date were censored at their last contact date and participants with survival data obtained after the planned analysis data cut-off date had survival censored at the cut-off date.

Intent to Treat (ITT) Analysis Set (all randomized participants); participants in the ITT Analysis Set were required to have wild-type KRAS exon 2 (codons 12 and 13, alleles G12A, G12D, G12R, G12C, G12S, G12V, or G13D) per protocol.

Progression-free survival (PFS) was defined as the time from the randomization date to the date of disease progression per Response Evaluation Criteria In Solid Tumors (RECIST) version 1.1 or death. Progressive disease (PD): At least a 20% increase in the size of target lesions compared with the smallest size since treatment started and an absolute increase of at least 5 mm, any new lesions or an increase in size of non-target lesions thought be ≥ 20% and an absolute increase of at least 5 mm, or significant increase in pleural effusions, ascites or other fluid collections with cytologic proof of malignancy. Participants who were alive and did not meet the criteria for progression by the analysis data cut-off date were censored at their last evaluable disease assessment date.

ITT Analysis Set

A secondary efficacy endpoint was overall survival in participants with wild-type rat sarcoma viral oncogene homolog (RAS) (without mutation in exons 2 [codons 12 and 13], 3 [codons 59 and 61], and 4 [codons 117 and 146] of KRAS and neuroblastoma RAS viral oncogene (NRAS)). In participants with wild-type RAS, RAS mutation status was defined by KRAS exon 2 mutation status per clinical trial assay testing and mutation status of KRAS exon 3 and 4 and NRAS exons 2, 3 and 4 per Sanger bi-directional sequencing. Overall survival was defined as the time from the randomization date to the date of death. Participants who had not died by the analysis data cut-off date were censored at their last contact date and participants with survival data obtained after the planned analysis data cut-off date had survival censored at the cut-off date.

Wild-type RAS Efficacy Analysis Set (subset of participants in the ITT Analysis Set without mutation in exon 2, 3, and 4 of KRAS or NRAS)

PFS was defined as the time from the randomization date to the date of disease progression per RECIST version 1.1 or death.

Progressive disease (PD): At least a 20% increase in the size of target lesions compared with the smallest size since treatment started and an absolute increase of at least 5 mm, any new lesions, or an increase in size of non-target lesions thought be ≥ 20% with an absolute increase of at least 5 mm, or significant increase in pleural effusions, ascites or other fluid collections with cytologic proof of malignancy. Participants who were alive and did not meet the criteria for progression by the analysis data cut-off date were censored at their last evaluable disease assessment date.

Wild-type RAS Efficacy Analysis Set

Objective response rate (ORR) is defined as the percentage of participants with either a complete response (CR) or partial response (PR) per RECIST version 1.1. Radiographic tumor assessments and investigator's assessment of response were performed at Week 4, Week 8, and then every 8 weeks until disease progression (radiographic or clinical progression). CR: Disappearance of all target and non-target lesions and no new lesions. Any pathological lymph nodes (whether target or non-target) must have reduction in short axis to < 10 mm. PR: At least a 30% decrease in the size of target lesions with no progression of non-target lesions and no new lesions, or, the disappearance of all target lesions with persistence of one or more non-target lesions not qualifying for either CR or PD and no new lesions.

ITT analysis set

Objective response rate is defined as the percentage of participants with either a complete response (CR) or partial response (PR) per RECIST version 1.1. Radiographic tumor assessments and investigator's assessment of response were performed at Week 4, Week 8, and then every 8 weeks until disease progression (radiographic or clinical progression). CR: Disappearance of all target and non-target lesions and no new lesions. Any pathological lymph nodes (whether target or non-target) must have reduction in short axis to < 10 mm. PR: At least a 30% decrease in the size of target lesions with no progression of non-target lesions and no new lesions, or, the disappearance of all target lesions with persistence of one or more non-target lesions not qualifying for either CR or PD and no new lesions.

Wild-type RAS Efficacy Analysis Set

The severity of each AE was graded according to the Common Terminology Criteria for Adverse Events (CTCAE) version 3.0 (Grade 1 = Mild; 2 = Moderate (discomfort enough to cause interference with usual activity); 3 = Severe (incapacitating with inability to work or do usual activity); 4 = Life-threatening and 5 = Fatal), with the exception of the skin-or nail-related AEs which were graded using a CTCAE version 3.0 with modifications. A serious AE was defined as an AE that met at least 1 of the following criteria: • fatal, • life-threatening, • required in-patient hospitalization or prolongation of existing hospitalization, • resulted in persistent or significant disability/incapacity, • congenital anomaly/birth defect, and/or • other medically important serious event. Treatment-related AEs (TRAEs) are those the investigator considered there was reasonable possibility that the event might have been caused by study drug.

Safety Analysis Set (all randomized participants)

QT interval is a measure of the time between the start of the Q wave and the end of the T wave in the heart's electrical cycle as measured by electrocardiogram (ECG). QTc is the QT interval corrected for heart rate. To evaluate the effect of panitumumab treatment on the QTc interval length among participants treated with panitumumab, ECGs were collected at the following time points from participants randomized to panitumumab arm at a limited number of sites: Week 1 prior to the first panitumumab infusion (Baseline) and within 30 minutes following the end of the first infusion of panitumumab (Cmax), Week 7 after 3 doses of panitumumab (steady state), and at the safety follow-up visit. The ECGs were submitted for independent central review to calculate the reported QTc interval. QTc was calculated using both the Bazett correction (QTcB) and the Fridericia correction (QTcF).

QTc Analysis Set is defined as the subset of participants in the Safety Analysis Set who received at least one panitumumab dose and were enrolled at the limited number of sites participating in QTc evaluation and had baseline and at least 1 post-baseline QTc assessment.