[Isolated tumor cells and micrometastasis--clinical behavior and therapeutic implications]

Recent advances in the detection of both isolated tumor cells and micrometastases in distant organs by means of immunocytochemical and molecular biological techniques have brought a new paradigm for the understanding of cancer biology. For instance, although the presence of a micrometastasis is a significant indicator of poor prognosis, it is now widely accepted that certain residual tumor cells remain dormant for a long period without any treatment. Many investigators have focused on what is different in the nature of the dormant and active tumor cells, and how microtumors can acquire the active phenotype in ectopic distant organs. In addition, information on both isolated tumor cells and micrometastases is useful not only for staging but also for considering an adjuvant treatment schedule. This review summarizes the recent clinical outcomes of the investigations of both isolated tumor cells and micrometastases.