Circulating tumor cells and their clinical significance

Metastases to other organs and the formation of secondary tumors are responsible for 90% of cancer-related deaths. However, even in the early stages of cancer, about 30–40% of patients with localized disease may have latent metastasis, which are likely derived from circulating tumor cells (CTCs) involved in disease progression. Therefore, detection and analysis of CTCs can play an important role in the diagnosis and decision-making of adjuvant treat­ment that aims to prevent metastasis. At present, patients’ selection of treatment is based on the statistical risk of recurrence of metastatic disease, without considering whether the tumor cells have spread from the primary tumor. This may lead to unnecessary treatment of non-metastatic disease patients. Therefore, early detection of CTCs in the blood is critically important, and should allow for a more accurate assessment of disease severity. Here, we provide an overview of CTC phenotypes, including plasticity of CTCs, and their clinical significance.