[Development of minimal residual cancer cell research]

Micrometastases of cancer cells occur during the early stages of cancer or from minimal residual cancer cells with metastatic potential. Recent progress in measuring methods has enabled the detection of minimal residual cancer cells in areas such as circulating tumor cells (CTCs) in peripheral blood, disseminated tumor cells in bone marrow, and free tumor cells in lymph nodes and the peritoneal cavity. Recently, it has been reported that the phenotypes of CTCs are closely related to cancer stem cells, and thus they may be of interest as new biomarkers in cancer patients. The usefulness of CTCs as predictive markers for recurrence and prognosis was demonstrated in patients with breast and colorectal cancer. Progress in the early diagnosis of the therapeutic effects of chemotherapy combined with molecular targeted drugs has also been enhanced by the detection of CTCs. Furthermore, individualized, limited surgery based on sentinel node navigation surgery has been performed not only in patients with breast cancer but also in those with gastric cancer. The clinical significance of free tumor cells in the peritoneal cavity of colorectal cancer patients has also become an area of interest. These developments in minimal residual cancer cell research may lead to a new metastatic cascade concept and novel approaches to cancer therapy.