Patients' selection thorough the identification of predictive factors still represent a challenge in metastatic colorectal cancer (mCRC). Cetuximab (Erbitux®), a chimeric monoclonal antibody binding to the Epidermal Growth Factor Receptor (EGFR), belongs to the Immunoglobulins (Ig) grade 1 subclass able to elicit both in vitro and in vivo the Antibody-Dependent Cell-mediated Cytotoxicity (ADCC). ADCC is the cytotoxic killing of antibody-coated target cells by immunologic effectors. The effector cells express a receptor for the Fc portion of these antibodies (FcγR); genetic polymorphisms of FcγR modify the binding affinity with the Fc of IgG1 (Immunoglobulins Gamma subclass 1). Interestingly, the high-affinity FcγRIIIa (FcγR type IIIa) V/V is associated with increased ADCC in vitro and in vivo. Thus, ADCC could partially account for cetuximab activity. CIFRA is a single arm, open-label, phase II study assessing the activity of cetuximab in combination with irinotecan and fluorouracile in FcγRIIIa V/V patients with KRAS (Kirsten RAt Sarcoma), NRAS (Neuroblastoma Rat Sarcoma), BRAF (B-Rapidly Accelerated Fibrosarcoma) wild type mCRC. The study is designed with a two-stage Simon model based on a hypothetical higher response rate (+10%) of FcγRIIIa V/V patients as compared to previous trials (about 60%) assuming ADCC as one of the mechanisms of cetuximab action. The test power is 95%, the alpha value of the I-type error is 5%. With these assumptions the sample for passing the first stage is 14 patients with \>6 responses and the final sample is 34 patients with \>18 responses to draw positive conclusions. Secondary objectives include toxicity, responses' duration, progression-free and overall survival. Furthermore, an associated translational study will assess the patients' cetuximab-mediated ADCC and characterize the tumor microenvironment. The CIFRA study will determine whether ADCC contributes to cetuximab activity in mCRC patients selected on an innovative immunological screening. Data from the translational study will support results'interpretation as well as provide new insights in host-tumor interactions and cetuximab activity.