FOLFIRI chemotherapy was initiated on Day 1 of each treatment cycle at the following starting doses: irinotecan 180 mg/m^2, leucovorin 400 mg/m^2 racemate (or 200 mg/m^2 I-leucovorin), 5-FU bolus 400 mg/m^2, 5-FU infusion 2400 mg/m^2.

Time to progression was defined as the time from the randomization date to the date of first observed disease progression per the modified RECIST criteria. Participants not meeting these criteria by the analysis data cutoff date were censored at their last evaluable disease assessment date.

Progressive disease is defined as a ≥ 20% increase in the size of target lesions or unequivocal progression of existing non-target lesions or any new lesions.

Calculated only for those participants with an objective response as the time from the first objective response (subsequently confirmed within no less than 4 weeks) to first observed disease progression per modified-RECIST criteria. Participants not meeting these criteria by the analysis data cutoff date were censored at their last evaluable disease assessment date.

Progressive disease is defined as a ≥ 20% increase in the size of target lesions or unequivocal progression of existing non-target lesions or any new lesions.

A serious adverse event (SAE) is defined by regulatory authorities as one that • is fatal • is life threatening (places the subject at immediate risk of death) • requires in-patient hospitalization or prolongation of existing hospitalization • results in persistent or significant disability/incapacity • is a congenital anomaly/birth defect • other significant medical hazard. The relationship of the adverse event to the study treatment was assessed by the Investigator by means of the question: "Is there a reasonable possibility that the event may have been caused by the study treatment?"

Total of all reporting groups

KRAS, the human homolog of the Kirsten rat sarcoma-2 virus oncogene

mCRC: metastatic colorectal cancer

Grade 0: Fully active, able to carry on all pre-disease performance without restriction; Grade 1: Restricted in physically strenuous activity but ambulatory and able to carry out work of a light or sedentary nature; Grade 2: Ambulatory and capable of all self-care but unable to carry out any work activities. Up and about > 50% of waking hours; Grade 3: Capable of only limited self care, confined to a bed or chair > 50% of waking hours; Grade 4: Completely disabled. Cannot carry on any self-care. Totally confined to bed or chair; Grade 5: Dead

Participants with wild-type KRAS were randomized to FOLFIRI chemotherapy regimen administered in cycles every two weeks.

Participants with mutant KRAS were randomized to 6 mg/kg panitumumab plus FOLFIRI chemotherapy regimen administered in cycles every two weeks.

Participants with mutant KRAS were randomized to FOLFIRI chemotherapy regimen administered in cycles every two weeks.

Overall survival was defined as the time from randomization to the date of death. Participants who had not died by the analysis data cutoff date had their time of death censored at their last contact date.

KRAS Efficacy Analysis Set

Participants were evaluated for tumor response per the modified Response Evaluation Criteria in Solid Tumors (RECIST) criteria every 8 weeks until disease progression. Objective response was defined as the incidence of either a confirmed complete or partial response (CR or PR) while on study, as determined by blinded independent central review and confirmed no less than 4-weeks after the criteria for response are first met. CR: Disappearance of all target and non-target lesions and no new lesions. PR: At least a 30% decrease in the sum of the longest diameter of target lesions and no progression of non-target or no new lesions, or, disappearance of all target lesions and the persistence of ≥ 1 non-target lesion not qualifying for either CR or progressive disease. Participants without a post-baseline assessment were considered non-responders.

KRAS Central Tumor Response Analysis Set: subset of participants with at least one uni-dimensionally measurable lesion per the modified RECIST criteria per blinded central radiology review for whom KRAS was assessed.

Time to progression was defined as the time from the randomization date to the date of first observed disease progression per the modified RECIST criteria. Participants not meeting these criteria by the analysis data cutoff date were censored at their last evaluable disease assessment date.

Progressive disease is defined as a ≥ 20% increase in the size of target lesions or unequivocal progression of existing non-target lesions or any new lesions.

KRAS Efficacy Analysis Set

Calculated only for those participants with an objective response as the time from the first objective response (subsequently confirmed within no less than 4 weeks) to first observed disease progression per modified-RECIST criteria. Participants not meeting these criteria by the analysis data cutoff date were censored at their last evaluable disease assessment date.

Progressive disease is defined as a ≥ 20% increase in the size of target lesions or unequivocal progression of existing non-target lesions or any new lesions.

KRAS Central Tumor Response Analysis Set: Responders

A serious adverse event (SAE) is defined by regulatory authorities as one that • is fatal • is life threatening (places the subject at immediate risk of death) • requires in-patient hospitalization or prolongation of existing hospitalization • results in persistent or significant disability/incapacity • is a congenital anomaly/birth defect • other significant medical hazard. The relationship of the adverse event to the study treatment was assessed by the Investigator by means of the question: "Is there a reasonable possibility that the event may have been caused by the study treatment?"

Safety analysis set: all participants who received at least 1 dose of panitumumab or chemotherapy. One participant was randomized to Panitumumab Plus FOLFIRI, but received FOLFIRI Alone and is included in the FOLFIRI Alone group for safety analyses.

Participants received FOLFIRI chemotherapy regimen administered in cycles every two weeks.