- Histological diagnosis of un-resectable or metastatic colorectal cancer which is KRAS and NRAS mutation negative (wild-type). Patients with any known mutation in KRAS or NRAS codons 12, 13, 59, 61, 117 or 146 will be excluded. Mutations of KRAS and NRAS codons not listed above are allowed. Biopsy of metastatic lesion is not required.