Micrometastasis in gastric cancer

Circulating tumor cells (CTCs) are a crucial contributor and indicator for cancer metastasis. The presence of CTCs and other two forms of occult disease including circulating tumor microembolus (CTMs) as well as disseminated tumor cells (DTCs) as a sign for micrometastasis has been associated with adverse survival of both localized and metastatic cancers. However, their assignments in micrometastasis are still not well understood. This mini-review is aimed to provide an overview of the biological features and the clinical impact of CTCs, DTCs and CTM in gastric cancer (GC), and to summarize the technical limitations of detection methods in addition to the significance of distinct migration modes in epithelial-mesenchymal transition (EMT) and gastric micrometastasis. Although there are controversies over current CTC identification strategies, both single and collective migration modes as indispensable parts of micrometastasis are influential participants in GC progression, diagnosis and prognosis. CTCs, CTM and DTCs are not separated forms of the occult disease; however available techniques fail to detect all subsets of them. Therefore, micrometastatic detection should be combined with conventional pathological examinations in order to make more accurate predictions of tumor outcomes. Novel markers further defining the features of CTC subsets are warranted.