On the basis of research results of the past few decades, it is widely accepted that tumor-derived cells (CTCs) or circulating tumor-derived nucleic acids (ctNAs) found in the circulation of cancer patients might be a sign of micrometastases and thus could be an important predictor of prognosis. It is possible to estimate CTCs/ctNAs by immunocytochemical or molecular assays and these assays might also be used to monitor signs not only systemically but also in real-time in patients with malignant tumors. In this article, we discuss the transition of CTCs/ctNAs from the research setting to clinical application in oral cancer, especially our current research findings. Key words:circulating tumor-derived cells, circulating tumor-derived nucleic acids, mitochondrial DNAs, micro metas tasis, oral cancer prognosis