The article provides a comprehensive review of the emerging biological principles underlying cancer metastasis, focusing on carcinomas where the most research has been conducted. Metastasis, the process by which cancer cells spread from the primary tumor to distant sites, remains a significant challenge in cancer biology due to its complexity. The review highlights the importance of the epithelial-mesenchymal transition (EMT) in enabling cancer cells to acquire traits necessary for dissemination, such as increased motility and invasiveness. However, the role of EMT in metastasis is complex and not fully understood, with some studies suggesting that other cell-biological programs may also play a role. The article discusses the dissemination of carcinoma cells, including the role of collective migration and the partial EMT state, which may enhance tumor progression and metastasis. It also explores the interactions of circulating tumor cells (CTCs) with the immune system, particularly platelets and neutrophils, which can either protect or facilitate the survival and spread of cancer cells. The process of extravasation, the ability of CTCs to enter and colonize distant tissues, is examined, along with the factors that influence this step, such as vascular permeability and the recruitment of monocytes. The review further delves into the concept of metastatic dormancy, where disseminated tumor cells (DTCs) remain quiescent for extended periods, and the niche in which they reside, which can provide resistance to therapeutic agents. The role of cancer stem cells (CSCs) in initiating metastatic colonization is emphasized, as these cells possess the ability to reinitiate tumor growth at distant sites. The article concludes by discussing the paradox of carcinoma metastases retaining epithelial features despite the mesenchymal nature of the disseminating cells, which is resolved by the reverse process of mesenchymal-epithelial transition (MET). Overall, the review underscores the emerging biological principles that underlie the metastatic process, highlighting the need for further research to better understand and potentially prevent this deadly aspect of cancer.The article provides a comprehensive review of the emerging biological principles underlying cancer metastasis, focusing on carcinomas where the most research has been conducted. Metastasis, the process by which cancer cells spread from the primary tumor to distant sites, remains a significant challenge in cancer biology due to its complexity. The review highlights the importance of the epithelial-mesenchymal transition (EMT) in enabling cancer cells to acquire traits necessary for dissemination, such as increased motility and invasiveness. However, the role of EMT in metastasis is complex and not fully understood, with some studies suggesting that other cell-biological programs may also play a role. The article discusses the dissemination of carcinoma cells, including the role of collective migration and the partial EMT state, which may enhance tumor progression and metastasis. It also explores the interactions of circulating tumor cells (CTCs) with the immune system, particularly platelets and neutrophils, which can either protect or facilitate the survival and spread of cancer cells. The process of extravasation, the ability of CTCs to enter and colonize distant tissues, is examined, along with the factors that influence this step, such as vascular permeability and the recruitment of monocytes. The review further delves into the concept of metastatic dormancy, where disseminated tumor cells (DTCs) remain quiescent for extended periods, and the niche in which they reside, which can provide resistance to therapeutic agents. The role of cancer stem cells (CSCs) in initiating metastatic colonization is emphasized, as these cells possess the ability to reinitiate tumor growth at distant sites. The article concludes by discussing the paradox of carcinoma metastases retaining epithelial features despite the mesenchymal nature of the disseminating cells, which is resolved by the reverse process of mesenchymal-epithelial transition (MET). Overall, the review underscores the emerging biological principles that underlie the metastatic process, highlighting the need for further research to better understand and potentially prevent this deadly aspect of cancer.