Panitumumab Regimen Evaluation in Colorectal Cancer to Estimate Primary Response to Treatment

Objective response rate is defined as the percentage of participants with a best response of complete response or partial response. Disease assessments were based on investigator review of scans using modified Response Evaluation Criteria in Solid Tumors (RECIST) criteria. A complete or partial response was confirmed no less than 4 weeks after the criteria for response were first met. Participants with no radiographic tumor assessment(s) at Week 17 or 25 were considered non-responders. Complete Response (CR): disappearance of all target and non-target lesions and no new lesions. Partial Response (PR): At least a 30% decrease in the size of target lesions with no progression of non-target lesions (defined as a ≥ 25% increase in lesion size) and no new lesions, or, the disappearance of all target lesions but persistence of 1 or more non-target lesions not qualifying for either CR or progressive disease (PD) and no new lesions.

Objective response rate is defined as the percentage of participants with a best response of complete response or partial response based on investigator review of scans using modified RECIST criteria. A complete or partial response was confirmed no less than 4 weeks after the criteria for response were first met. Participants with no post-baseline radiographic tumor assessment(s) were considered non-responders.

CR: disappearance of all target and non-target lesions and no new lesions. PR: At least a 30% decrease in the size of target lesions with no progression of non-target lesions (defined as a ≥ 25% increase in lesion size) and no new lesions, or, the disappearance of all target lesions but persistence of 1 or more non-target lesions not qualifying for either CR or PD and no new lesions.

The progression-free survival rate is defined as the Kaplan-Meier (KM) estimator of progression-free survival at Week 17 and Week 25 reported as the probability of being event (disease progression or death)-free. Tumor assessments were evaluated by the investigator according to modified RECIST criteria.

PD: At least a 20% increase in the size of target lesions since the treatment started or at least a 25% increase in the size of non-target lesions and the lesion(s) measure ≥ 10 mm, or the appearance of any new lesions. Participants who withdraw from the study prior to completion of Week 17 or 25 radiographic tumor assessments were censored at the last evaluable tumor assessment.

Progression-free survival time was defined as the time from Study Day 1 to the date of disease progression (based on investigator assessment) or the date of death due to any cause. Participants who terminated from the study early (eg, prior to disease progression due to fully withdrawn informed consent) were censored at their last tumor assessment.

The percentage of participants whose best response was either a complete or partial response or stable disease, based on modified RECIST criteria as assessed by the investigator. Stable diease (SD): Neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for PD of target lesions and no progression of existing non-target lesions and no new lesions, or, the persistence of 1 or more non-target lesions not qualifying for either CR or PD if no target lesions were identified at Baseline.

Duration of response is defined as the time from the date of first response to the date of first progression of disease during second-line treatment (as evaluated by the investigator) or death (if the death was due to disease progression but not detected earlier) in the subset of participants who responded (CR or PR, as evaluated by the investigator). Duration of response was analyzed using Kaplan-Meier methods; participants who responded but did not progress while on study were censored at the date of last tumor assessment.

Overall survival is defined as as the number of days from Study Day 1 to the date of death due to any cause. Overall survival was analyzed using the Kaplan-Meier method; participants who were lost to follow-up or who had not died at the end of the study (52 weeks after the last participant was enrolled) were censored at the date of last contact.

Time to failure of second-line treatment is defined as the time from study Day 1 to the date of the earliest of the following events: end of second-line therapy due to any reason except for complete response and curative surgery; progressive disease; or death due to any cause. Time to treatment failure was analyzed using Kaplan-Meier methods; participants who did not discontinue second-line treatment or discontinue due to complete response or curative surgery, who were still alive, and who did not have disease progression were censored at the date of the last contact.

Time to progression is defined as the time from study Day 1 to the date of observed disease progression. Time to progression was analyzed using Kaplan-Meier methods; participants who did not have disease progression were censored at the date of last evaluable tumor assessment.

Time to response of second-line treatment is defined as the time from study Day 1 to the date of first documentation of CR or PR, calculated for those participants with an objective tumor response of CR or PR.

The severity of adverse events (AEs) was graded according to the National Cancer Institute (NCI) Common Terminology Criteria for Adverse Events (CTCAE) version 3.0, except for panitumumab related skin toxicities, where Grade 1 = Mild AE; Grade 2 = Moderate AE; Grade 3 = Severe AE; Grade 4 = Life-threatening or disabling AE; Grade 5 = Death related to AE. The relationship of each adverse event to the panitumumab and/or FOLFIRI regimen was assessed by the investigator. A serious adverse event was defined as an adverse event that • is fatal • is life threatening • 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.

Laboratory toxicities were graded according to CTCAE version 3.

The immunogenicity of panitumumab was evaluated using 2 different screening immunoassays for the detection of anti-panitumumab antibodies: an acid dissociation bridging enzyme-linked immunosorbent assay (ELISA; detecting high-affinity antibodies) and a Biacore® biosensor immunoassay (detecting both high and low-affinity antibodies). When either of the 2 screening assays yielded a positive result, that particular sample was subjected to an in vitro bioassay for the detection of neutralizing antibodies.