During the past decade, the molecular mechanisms in the process of tumor progression, including metastasis and angiogenesis, have become better understood. Cancer metastasis consists of multiple, complex interacting steps. Each of these steps is crucial and limiting, since a failure to complete any one prevents the tumor cell from producing a metastasis. Detachment from the solid tumor by loosening the intercellular junctions and proteolysis of the extracellular matrix enables tumor cells to enter blood- and lymph vessels. The intravasation into the circulation is supported by the secretion of angiogenic factors, which induce degradation of the basal membrane in blood vessels. Adhesion to endothelial cells, extravasation from the circulation, and induction of angiogenesis are further essential steps for completing the metastatic process. Furthermore, it is well known that once a tumor cell has entered circulation, it will survive only by evasion of the immune system. The systematic identification of tumor antigens opens up new possibilities for immunotherapeutic approaches.