Response prediction of third-line cetuximab-based therapy for patients with metastatic colorectal cancer using Fludeoxyglucose (FDG) Positron Emission Tomography/Computed Tomography (PET/CT)

Interventions: FDG PET/CT imaging on a dedicated PET/CT system (Siemens Biograph) is to be performed at baseline, and after one cycle and four cycles of Cetuximab therapy. CT is to be performed every 3 months to determine the progression-free survival. Patients will be followed up for at least one year. The FDG PET/CT imaging is non-invasive but requires the patients to fast for 6 hours before the examination and takes up to 3-hour stay. Primary outcome(s): Predictive value of response evaluation (including changes of SUV and MTV values) by FDG PET/CT for progression-free survival (assessed by RECIST criteria 1.1)[All participants be assessed for progression-free survival every 3 months by CT scans (RECIST criteria 1.1) up to one year after enrollment] Study Design: Purpose: Natural history;Duration: Longitudinal;Selection: Defined population;Timing: Prospective