 A central problem remains the impossibility to adequately predict the response to surgery, chemotherapy, radiochemotherapy, peptid-receptor-based Radiotherapy or biotherapy, precluding an individualized therapy precision medicine Rinke et al., 2014. An actual research topic in these patients is the identification of patient markers allowing an response prediction. Moreover, researchers try to identify tumor markers in patients with unknown primary in order to locate the origin of metastases. Further, identification of tumor specific markers would allow the development of screening strategies in GEP-NEN. Due to the ability of these techniques to describe the biological heterogenity of a tumor, proteomics protein based analysis methods are promising in the present problematic Bezabeh et al., 2014; Löhr et al., 2006; Pan et al., 2013. 