Dose-limiting toxicities (DLTs)=serious drug side effects preventing further dose escalation. If 1 of the first 3 subjects developed a DLT during cycle 1 up to 3 additional subjects were enrolled at that dose level. The maximum dose level at which DLTs occurred in fewer than 2 out of 3 to 6 subjects was defined as the Maximum Tolerated Dose (MTD).

All treated subjects

The single dose pharmacokinetics (PK) of cetuximab was administered with an intravenous dose of irinotecan 16 to 20 mg/m2; Cmax was evaluated based on concentration-time profile.

The single dose PK of cetuximab was administered with an intravenous dose of irinotecan 16 to 20 mg/m2; AUC(INF) was evaluated based on concentration-time profile.

The single dose PK of cetuximab was administered with an intravenous dose of irinotecan 16 to 20 mg/m2; T-half was evaluated based on concentration-time profile.

The single dose PK of cetuximab was administered with an intravenous dose of irinotecan 16 to 20 mg/m2; CL/BSA was evaluated based on concentration-time profile.

The single dose PK of cetuximab was administered with an intravenous dose of irinotecan 16 to 20 mg/m2; VSS/BSA was evaluated based on concentration-time profile.

Non-central nervous system (CNS) tumors evaluated using Response Evaluation Criteria In Solid Tumors (RECIST), criteria to define when cancer patients improve ("respond"), stay the same ("stable"), or worsen ("progression"). CNS tumors evaluated based on measurements by investigator, dependence on corticosteroids, and neurologic exam.

All treated subjects

In order to be considered positive for anti-cetuximab a sample had to: 1) be evaluable (i.e., have a pre and at least one post-treatment timepoint), 2) have an anti-cetuximab value > 7 ng/mL and 3) have a post-treatment sample at least twice the pre-treatment level.

Cohort comprises all enrolled participants who were tested for HACA. Evaluable participants had normal baseline HACA (≤ 7 ng/dL) and ≥1 postbaseline HACA levels; unevaluable participants either did not have enough sample for analysis or did not have a pre- and postinfusion sample for immunogenicity.

Toxicity assessments performed at least weekly from the 1st dose of study drug until at least 30 days after the final dose of study drug and thereafter every 4 weeks until all study-related toxicities resolved, returned to baseline, or were deemed irreversible, whichever was longer. Grade 3=severe AE; grade 4=disabling or life threatening.

All treated patients

MTD of cetuximab intravenous (IV) weekly + irinotecan IV x5 days x2 weeks (in a 3-week cycle) and RPIID of cetuximab IV weekly, as measured by dose-limiting toxicities (see outcome measure 2)

As-treated population

Blood samples were collected at selected times (pretreatment visit, prior to each treatment cycle, weekly, and at the end of treatment) for clinical laboratory evaluations. Grade 3= Severe AE; Grade 4=Life-threatening or disabling AE

Blood samples were collected at selected times (pretreatment visit, prior to each treatment cycle, weekly, and at the end of treatment) for clinical laboratory evaluations. Grade 3= Severe and undesirable AE; Grade 4=Life-threatening or disabling AE

Blood samples collected at selected times (pretreatment visit, prior to each treatment cycle, weekly, and at the end of treatment) for clinical laboratory evaluations. Grade 3= Severe AE; Grade 4=Life-threatening or disabling AE

Blood samples were collected at selected times (pretreatment visit, prior to each treatment cycle, weekly, and at the end of treatment) for clinical laboratory evaluations. Grade 3= Severe AE; Grade 4=Life-threatening or disabling AE