Early Biomarker With 18F-FDG PET for Treatment Optimization of Anti-EGFR Therapy in Patients With Metastatic Colorectal Cancer.

3rd line standard treatment of patients with metastatic colorectal cancer (CRC) harboring K-ras wild type consists of anti-EGFR treatment with either cetuximab or panitumumab. This type of treatment has a modest but significant beneficial activity in this patient group with improved progression-free and overall survival. Although it is well known that patients with advanced CRC harboring a K-Ras mutation will not respond to anti-EGFR treatment, it is not understood why patients with K-Ras wild type CRC do not all benefit from this type of therapy. In order to optimize treatment of these patients as well as health care costs, it is extremely important to identify those patients who will respond to treatment with an EGFR inhibitor at an early stage. The investigators hypothesize that the differences in response to treatment with cetuximab are due to variability in the pharmacokinetics and -dynamics of the antibody. Thus, the investigators hypothesize that patients who do not respond to anti-EGFR treatment, have insufficient drug levels in tumor tissue. The investigators hypothesize that this is due to pharmacodynamic processes such as sequestration of cetuximab in the liver which expresses high levels of EGF receptor. The phase I part of the study was fulfilled after inclusion of 36 patients to evaluate the potential applicability of the 89Zr-cetuximab PET as predictive marker for (absence of) response to cetuximab. Along with this analysis, FDG-PET evaluation before and after 1 administration of cetuximab was being performed. While we observed no correlation of 89Zr-cetuximab tumor uptake with clinical benefit in these 36 patients, we did find a clinical significant predictive value for the absence of response with early 18F-FDG-PET with the lack of clinical benefit at 2 months of treatment in this group of patients. Early 18F-FDG PET response evaluation shows great potential to be a clinically applicable tool to stop an ineffective treatment in a very early phase