ll; The incidence of binding antibodies (excluding predose positive patients) was 1.0% as detected by the acid-dissociation ELISA and < 1% as detected by the Biacore assay;
• The incidence of neutralising antibodies (excluding predose positive patients) was < 1%;
• No evidence of an altered safety profile was found in patients who tested positive for antibodies to Vectibix.
The detection of antibody formation is dependent on the sensitivity and specificity of the assay. The observed incidence of antibody positivity in an assay may be influenced by several factors including assay methodology, sample handling, timing of sample collection, concomitant medications and underlying disease, therefore, comparison of the incidence of antibodies to other products may be misleading.
Clinical efficacy as monotherapy
The efficacy of Vectibix as monotherapy in patients with metastatic colorectal cancer (mCRC) who had disease progression during or after prior chemotherapy was studied in a randomised controlled trial (463 patients) and open-label, single-arm trials (384 patients).
A multinational, randomised, controlled trial was conducted in 463 patients with EGFR-expressing metastatic carcinoma of the colon or rectum after confirmed failure of oxaliplatin and irinotecan-containing regimens. Patients were randomised 1:1 to receive Vectibix at a dose of 6 mg/kg given once every two weeks plus best supportive care (not including chemotherapy) (BSC) or BSC alone. Patients were treated until disease progression or unacceptable toxicity occurred. Upon disease progression BSC alone patients were eligible to crossover to a companion study and receive Vectibix at a dose of 6 mg/kg given once every two weeks.
Of 463 patients, 63% were male. The median age was 62 years (range 27 to 83), and 99% were Caucasian. Three hundred and ninety-six (86%) patients had a baseline ECOG Performance Status of 0 or 1. Sixty-seven percent of patients had colon cancer and 33% had rectal cancer.
The primary endpoint was progression-free survival (PFS). In an analysis adjusting for potential bias from unscheduled assessments, the rate of disease progression or death in patients who received Vectibix was reduced by 40% relative to patients that received BSC [Hazard Ratio = 0.60, (95% CI 0.49, 0.74), stratified log-rank p < 0.0001]. There was no difference seen in median PFS times as more than 50% of patients progressed in both treatment groups before the first scheduled visit.
The study was retrospectively analysed by wild-type KRAS status versus mutant KRAS status. KRAS mutation status was determined by analysis of archived paraffin embedded tumour tissue.
Tumour samples obtained from the primary resection of colorectal cancer were analysed for the presence of the seven most common activating mutations in the codon 12 and 13 (Gly12Asp, Gly12Ala, Gly12Val, Gly12Ser, Gly12Arg, Gly12Cys, and Gly13Asp) of the KRAS gene by using an allele-specific polymerase chain reaction. 427 (92%) patients were eva luable for KRAS status of which 184 had mutations. In an analysis adjusting for potential bias from unscheduled assessments the hazard ratio for PFS was 0.49 (95% CI: 0.37-0.65) in favour of panitumumab in the wild-type KRAS group and 1.07 (95% CI: 0.77-1.48) in the KRAS mutant group. The difference in median PFS in the wild-type KRAS group was 8 weeks. The progression-free survival rates at the first scheduled visit (week 8) in the wild-type KRAS group were 59.7% on Vectib |
