A phase II multicenter study of cetuximab monotherapy in patients with EGFR-undetectable refractory metastatic colorectal carcinoma (mCRC)

4065 Background: Cetuximab is a chimeric IgG1 Mab that targets the human epidermal growth factor receptor (EGFR). Most clinical trials using cetuximab in mCRC treated patients (pts) with EGFR positive tumors determined by immunohistochemistry (IHC). The intensity of EGFR immunostaining (IS) has not been related to the activity of cetuximab, and objective responses have been reported in pts with EGFR negative tumors. Potential reasons will be presented. Methods: This phase II multicenter study enrolled pts with refractory EGFR-undetectable mCRC who have received at least 1 standard fluoropyrimidine-containing chemotherapy regimen and an ECOG PS<2. Local results of EGFR by IHC were confirmed centrally. EGFR-undetectable disease is defined as no membrane staining above background for all tumor cells examined in a well preserved tissue section. Pts received weekly cetuximab infusions (400/250mg/m2 initial/weekly dose) and were evaluated for tumor response every 6 weeks. The primary outcome was overall respons...