Progression of malignant tumours to metastatic disease after surgery in curative intent is due to usually few and with conventional diagnostic techniques undetectable residual malignant cells. These cells must have been spread either before or during surgery. The more sensitive and specific detection of these malignant cells in various clinically relevant compartments of the patients organism became possible through new immunocytochemical and molecular tools. Various clinical studies underline the strong prognostic impact of the detection of disseminated cancer cells. However, many technical aspects did not yet allow sufficient standardization of these procedures and led to significantly varying results among different scientific groups. It is one of our primary aims to test, whether the detection of disseminated cancer cells might guide the indication for adjuvant therapies and might predict the efficacy of therapies in patients with solid cancers.