This overview mainly focuses on the topic of epithelial tumors (carcinomas) because urological tumors are generally of this type. The importance of the topic is reflected by the fact that patients rarely die of the primary tumor, but the majority die of metastases that cause life-threatening situations. More recent findings show that treatment decisions should be based on the metastasis site and less on the tumor's tissue of origin. Given the progression of clinical oncology toward individualized medicine, a better understanding of the biology of metastases is therefore acute and includes some important challenges.